Construction of China's Three Gorges Dam is likely to be finished by 20 May, nine months ahead of schedule, according to state media reports.
But several generators will still have to be installed and the dam is expected to become fully operational in 2009.
Once completed the dam, begun in 1993, will become the world's largest hydroelectric power project.
However, the $22bn scheme has been criticised for its high cost and the relocation of thousands of people.
"There are less than 3,000 cubic meters (105,000 cubic feet) of concrete left to be placed before the dam is finally completed," said Cao Guangjing, of China Yangtze River Three Gorges Project Development Corporation.
That would complete the principal part of the dam, which has often been compared to the Great Wall of China, Xinhua news agency reported.
China's government says the 7,600ft-long (2,300m) dam, will generate much needed power, prevent flooding and benefit shipping.
Critics say the dam's capacity to control floods is unproven and have also cited environmental problems.