China's outgoing ambassador to the World Trade Organization (WTO) said the nation's reform and opening-up should continue, but the future impetus will come from the inside, instead of foreign pressure.

The country has gradually adapted to WTO rules since entering the organization in 2001, said Sun Zhenyu on Tuesday, after ending his nine-year tenure as China's first envoy to the WTO.

Before being appointed ambassador, Sun was vice-minister of the Ministry of Foreign Trade and Economic Co-operation, the predecessor of the Ministry of Commerce.

China's foreign trade, which is expected to surpass $2.9 trillion this year due to a strong import and export rebound, has increased to about four times the 2001 trade volume.

The nation's adaptation to WTO obligations has been recognized by member countries, Sun said, though it also drew increasing criticism over the past two years for issues such as market access and government procurement.

"Some countries are more demanding now that China has become the world's second-largest economy and biggest exporter. But there's still room to further its reform and opening-up," he said.

"We have already done what we could do over the past nine years," he said.

"The next stage might be more difficult, considering the issues involved, because the reform is related to the redistribution of wealth," he said.

"Reform should continue, and the impetus should come from within rather than from the outside," he said.

Meanwhile, Sun urged countries to grasp what global leaders call the "window of opportunity" of 2011 to conclude the long-running Doha talks.

"If a conclusion to the whole Doha Round were achieved, it could help stimulate the recovery of the global economy," he said.

He called on the United States to take action to move beyond the stalemate and ensure that a global trade deal is reached.

US Democrats and Republicans should come to consensus and refocus on promoting trade, he said, and a global trade deal will help ease high unemployment and fulfill Washington's attempts to double US exports over the next five years.

Along with its robust trade and competitive advantage, China will remain a major target for protectionism as its trade continues to grow, Sun said.

In 2009, there were 127 cases filed by trade partners against China, the largest number ever, and during the first half of this year, 13 nations and regions initiated 37 cases against China.