In an exclusive interview, Lee placed high expectations on the ongoing bilateral FTA talks, which officially started in May.
The third round of dialogue concluded in late August in Weihai, Shandong province, and the fourth is planned to kick off in October, Yonhap News Agency said.
The ambassador said both sides are seeking a free-trade pact that "rules out unnecessary losses" in sensitive sectors and benefits both nations.
In recent months, farmers and fishermen in the ROK have protested that Chinese products pose a threat to their country's "fragile agricultural and fishery sectors".
The issue also came up during previous FTA talks between Seoul and other economies, including the European union , the United States and some South American countries, the ambassador said.
Lee expressed confidence that a compromise would be reached.
The first round of FTA talks started in mid-May, followed by a second round in July. According to Minister of Commerce Chen Deming, the negotiation process is expected to take two years.
Lee endorsed the rapidly developing ties between the two major Northeast Asian economies.
China is now the ROK's top export destination and import source, while the ROK is China's third-largest trade partner.
Statistics from the General Administration of Customs show that annual trade between the two nations climbed to $245.6 billion in 2011, a year-on-year increase of 18 percent.
During the 2012 Nuclear Security Summit in Seoul in late March, President Hu Jintao expressed confidence to his ROK counterpart Lee Myung-bak that bilateral trade will reach $300 billion by 2015.
The ROK ambassador said both nations have experienced difficulty in exporting to Europe amid the current global economic downturn.
"Yet trade and investment between China and the ROK has not been greatly affected, and in fact, investment is expanding," Lee said.
During a reception dinner attended by Vice-President Xi Jinping on Friday at the Great Hall of the People in Beijing commemorating the 20th anniversary of diplomatic ties, Lee hailed the two country's deepening strategic partnership.
He pointed to the 120 daily flights between the two countries and the more-than-70,000 students from the ROK studying in China. Lee expressed his hope that the trend will continue to grow.
