Abstract: Power flow calculation is the basis of analyzing the operating state of the system. The traditional power flow algorithm of the three-phase unbalanced system is mainly to solve the nonlinear power flow equation, and the calculation is complicated, and the convergence problem may occur if the initial value is not set properly. To solve the above problems, based on the time-domain iteration concept and the introduction of symmetric component analysis, a three-phase unbalanced microgrid power flow calculation method for the distributed generation(DG) unit is proposed. Firstly, the discrete operation model of sag control DG unit is established, and the output power of DG unit is calculated using time domain derivation instead of equations to avoid convergence problems. Secondly, the unbalanced three-phase three-wire system is decomposed into independent positive and negative sequence network based on the symmetric component method, and the feeder and load model of the positive and negative sequence network are established according to the network connection and network parameters. Then, the parallel iterative calculation of the positive and negative sequence complete network model is derived, which does not need to update the network matrix and reduces the scale of calculation. Finally, the algorithm is simulated based on IEEE-8 node system, and the corresponding Simulink model is established to verify the effectiveness of the algorithm.