The performances of two-stage double-clad Er3+/Yb3+ co-doped fiber amplifier（EYDFA）are analyzed based on the rate equation and light propagation equation.The optimum length and the influence of the ratio of forward and backward pump power on gain and noise characteristics of two-stage double-clad EYDFA are obtained with numerical simulation.The gain improvement of 4 dB and the noise figure reduction of 3 dB is obtained by choosing the optimum position of the isolator and the the ratio of forward and backward pump power.