More than 600 armed police have been working around the clock over the last six days on the canal cut out on the blockage.
By Saturday night, more than 340 soldiers and engineers have left Tangjiashan, officials said.
The first group of 15 workers, mainly soldiers of the hydropower corps of the People's Armed Police Force, left in a helicopter at 8:35 a.m. Saturday, a Xinhua reporter at the site said.
They were taken to the Nanjiao Military Airport in Mianyang City for rest, he said.
The remaining 300 people will stay through Saturday night, and most of them would leave by Sunday noon, said Zhou Xiangjun, an armed police officer. About 20 soldiers would stay at Tangjiashan to monitor the situation, he said.
On Saturday, the soldiers left in helicopters and some left on foot.
"We prefer the airlift if weather permits. If the weather turns bad, we will walk out tomorrow morning," said Yue Xi, deputy chief of hydropower corps.
It takes 40 minutes to reach the airport in Mianyang and six to seven hours by foot. Evacuees have to cross two mountains if they choose to walk out, he said.
A total of 197,477 people were evacuated to safe ground as of 8 a.m. Saturday in line with an emergency plan, an official with the quake relief headquarters of Mianyang City said.
Nearly 200,000 people evacuated to higher ground
Tan Li, Communist Party chief of Mianyang and head of Mianyang City Quake Control and Relief Headquarters, on Friday renewed an order that 1.3 million people living downstream from Tangjiashan must rehearse evacuation to higher ground demarcated by government departments in preparation for a worst-case scenario on Sunday, a day after originally planned Saturday.