China has built a number of dams recently, including the Three Gorges
China's environment ministry has suspended construction of two dams on a tributary of the Yangtze River.
The projects on the Jinsha River had been started without environmental assessments or approval from the ministry, officials said.
The dams are part of a series of eight power stations planned for the Jinsha.
The $30bn (£18bn) project has been criticised by conservationists, who say it will damage the region's environment and biodiversity.
The power stations are expected to generate as much electricity as the controversial Three Gorges Dam - about 20 gigawatts.
The series of hydro-electric stations is planned for a 560km (350 mile) stretch of the Jinsha River in south-west China's Yunnan province.
The dams suspended by the environment ministry at Longkaikou and Ludila were being built by two of China's largest power-generating companies - Huaneng Power and Huadian Power.
"To protect the management of the environment... and to punish the violation of the environment and illegal acts regarding the environment, the environmental ministry decided to suspend the construction projects in the middle reaches of the Jinsha River," a statement from the Ministry of Environmental Protection said.
The ministry also suspended approvals for the two companies' other projects, except those involving energy-saving and pollution prevention measures.
At the same time, the ministry said it was suspending construction projects in eastern Shandong province begun by a state-owned steel company because it had not submitted an environmental impact assessment.
Two other dams in the Jinsha River project have received approval from the environment ministry, but another dam planned for the Tiger Leaping Gorge area was suspended after a public outcry in 2005.
Tiger Leaping Gorge and the nearby town of Lijiang are popular with tourists and trekkers.
Further hydro-electric dams are also planned for elsewhere on the Yangtze River system, as Chinese authorities attempt to reduce their reliance on burning coal to produce power.