Abstract: The Xiluodu Hydropower Station on the Jinsha River is a giant hydropower stadon, but a thrust nappe structure--Majiahe Dam fault--lies in the reservoir head region. This fault, especially a swarm of klippen on the right bank of the river, will submerge when the hydropower station is in operation. Therefore it is very important to study the acdvity of the fault and make a stability assessment. Integrated fundamental geological, Quaternary geomorphological, seismic geological, hydrogeological and geochronological studies show that the Majiahe Dam fault is not an active fault, and the limit equilibrium analysis and calculation of the controlling secdon indicate that the swarm of klippen will generally maintain good stability under all construction conditions.