In this paper,an iterative algorithm model was proposed for nonlinear rate-equation of EYDFA.Based on the automatic gain feedback control strategy of ring cavity,the influence of pump power changes on automatic gain control of EYDFA under the WDM conditions was analyzed using the proposed model.The result shows that the controllable range of the signal gain increases gradually with increase of pump power.The analysis further shows that the peak of the gain drift also increases gradually with the increase of pump power when multi-channel signals were removed.