Abstract: If a comprehensive survey of river course of middle-lower reaches of the Min river and the hydrographic characteristics is made,the conclusion that the harmless effect on the ecological environment when a hydropower station is built at Shuikou Can be reached.The reasons are: 1.After the station is completed,most of the minerals and organic matters will still be washed away into the lower reaches during the flood stage since the torrent of the middle reaches will go on flowing downward in great quantities. 2.After the station is completed,the discharge of lower reaches during the low water stage will be increased by the adjustment,so that the movements of tidal current will be as regular as usual and that is more favourable than before for the irrigation and navigation. 8.After the station is completed,the ecological environment will be as same as before both at the mouth of the Min river and beyond it,so there will be no obvious effects on the migration of fishes and the fishing production. The problem of any sudden disappearance of fishes at the fishing ground owing to the shortage of baits will not at all occur. 4.A great quantity of mud and sand will be washed out from the middle reaches beyond the dam so that deposition of silt within the reservoirs must not be very serious.