At initial impoundment period, the water level in observation hole became high, the seepage amount was gradually increasing at the downstream of Jiangxiong reservoir dam and the abnormal phenomena appeared with maximum seepage amount of 300 L/s at the measuring weir, which affect the dam safety. Analysis was made on the major seepage causes of dam foundation, around-the-dam, spillway and water intake tunnel by dam observation system， electricity detection and interconnection test, the main seepage channels found to provide decision basis for dam impermeable scheme. And a view is also presented in this paper that safe seepage has enormous function to protect downstream ecology.