Abstract: A theoretical model of Er3+/Yb3+ co-doped fibre amplifier,based on the one of Er3+-doped fibre amplifier,as presented in this paper,by analysing some of the references concerned.The performances of the signal,the pump,and the amplified spontaneous emission(ASE)in the Er3+/Yb3+ co-doped fibre can be simulated with this model.Some of results from this model are significant and interesting.