The leader of the world's largest developed country came across the Pacific Ocean to the largest developing country this week, and nobody could ignore the event nor its significance.

As today's world is undergoing tremendous development and change, how China and the United States define their relations means much, not only to each other, but also to the rest of the world.

"The significance and influence of China-US relations go far beyond the two countries," Chinese President Hu Jintao has said.

Soon after she took office, US Secretary of State Hillary Clinton said that US-China relations would decide whether the 21st century international relationship is antagonistic or peaceful. US President Barack Obama has also stressed on several occasions that US-China relations would shape the 21st century.

Compared to the past, the current China-US relations have shown new characteristics.

Bilateral communication has been expanded geographically against the backdrop of globalization, and the contacts involving China and the United States occur everyday at almost every corner of the world, not just between the two countries.

Moreover, the content of the China-US communication has been expanded to every area, including politics, economy, military, culture and environmental protection, which is not limited to a certain field.

It's worth noticing that after entering the 21st century, the relationship between China and the United States has been increasingly intertwined with global issues, and the two nations have to face various global challenges together, not just problems of their own.

"The major challenges of the 21st century, from climate change to nuclear proliferation to economic recovery, are challenges that touch both our nations and challenges that neither of our nations can solve by acting alone," Obama said in Beijing after meeting the Chinese president on Tuesday.

As the China-US Joint Statement issued after the meeting of the two leaders pointed out, under the circumstance of the international situation undergoing profound and complex changes, China and the United States have common responsibilities on regional and global security issues.

China-US relations, the relationship of the world's largest developing and developed countries, reflect a new character along the evolution of world structure in this new century, that is, developing countries have been gaining more say and influence in the world, with their status on the international political and economic stage becoming more important.

In a changing world, the trend of China-US ties has impact on the well-being of the future world.

Through Obama's Asia tour and his first visit to China, it is easy to see that cooperation between China and the United States will not only benefit the two countries and the two peoples, but also conduce to peace, stability and prosperity of the Asia-Pacific region and the world as a whole. Such consensus has been reached by the leaders of the two countries.

Obama described China as both an important partner and a friendly competitor, saying the United States seeks cooperation, instead of confrontation, with China. He said the United States does not intend to contain China's rise and that he welcomes China as a "strong, prosperous and successful member of the community of nations."

It is on the basis of such consensus that Obama's China visit turned to be fruitful. The two countries reaffirmed the new definition of their ties -- a positive, cooperative and comprehensive relationship in the 21st century -- as established by their heads of state, and enriched their relations and cooperation with more strategic connotation.

The cooperation between China and the United States is indispensable for the world's development. It is presumable that the two countries' interests are to further intertwine and bilateral cooperation is to make continuous progress. However, the two sides must soberly deal with differences and contradictions at the same time.

Just as President Hu said, "it is normal for China and the United States to have some discrepancies since the conditions in the two countries are different, yet the most critical part lies in the respect of common interests and major concerns."

According to Hu, for an enhanced China-US relationship, it is primarily necessary to establish strategic mutual trust, and politicians of the two countries are required to "have enough strategic insight and political wisdom" and to make joint efforts, improve understanding, expand cooperation and deal properly with discrepancies so as to push China-US ties onto a new level.

"The Chinese side is willing to work with the US side to push for the sustained, sound and stable development of China-US ties so as to better benefit the peoples of the two countries and the world as well." These remarks by Hu conveyed not only the will of China, but also the expectation of the world.