1、将待求支路移开
2、求有源二端网络开路电压Uab
I1=E1/(R1+R3),I2=Is+E2/R2,Uab=I1*R3-E2+I2*R2
3,求等效电阻Rab=(R1//R3)+R5+R2
4,I=Uab/(Rab+R4)