The problem of P-n junction in Ref.[1] is discussed in this paper. We consider that Tsai Shu-tang's view that W.Shock-ley's equation cannot be applied to all circumstances is correct, but we cannot say, because of this, that W. Shockley's method of treatment and its conclusion for P-n junction are wrong. In this paper we demonstrated that W. Shockley's equation merely describes ideal P-n junction model.