Abstract: Various distributed generators（DGs） are integrated in distribution system which is usually operated in three-phase unbalanced condition. There are various distributed generator with various control mode. The equivalent interface impedance of DGs may vary within a large range. Backward/forward sweep power flow（FBS） is an important method for distribution system power flow analysis. In this paper, the convergence problem caused by the zero and negative sequence impedance of DGs in forward/backward sweep power flow was found through numerical experiments. The reason of this phenomenon is that spectral radius of FBS is more than 1 and an impedance compensation method is proposed to solve this problem.