A three-dimensional time-integrated bound ary-laryer model is designed to be applied fur Lake Biwa complex terrain, and an improved finite difference scheme procedure fur approximating horizontal derivatives in a terrain-following coordinate system is introduced.Under weak large-scale wind field,the authors add real Lake Biwa terrain to the model and the results show that the mudel computation is very stable and saves computing time.Meanwhile, some numerical experiments are made with giving consideration to such different factors as watershed terrain,the existence of lake, etc.Under strong large-scale wind field, the authors add smooth terrain of Lake Biwa to this model, and the results obtained are satisfactory.