Abstract: In recent years, due to continuous growth of distributed generation with dynamic and intermittent,feature Which has more impacts on the operation of power system. The integrated power grid modelling method combining transmission and distribution helps to establish an internal relationship between distribution and transmission systems. A joint simulation power flow model combining three-phase power transmission and distribution is proposed. Other joint simulation methods are also studied to analyze the anti-interference ability of the power grid voltage with imbalance and various load types in consideration. The results show that the stability margin of phase voltage can be calculated more accurately based on the three-phase power flow simulation method, so as to improve the overall power supply stability of each phase in the transmission and distribution network.