A method of three-phase probabilistic power flow for distribution systems with single-phase and three-phase grid-connected photovoltaic（PV） systems is introduced using sequential Monte Carlo techniques. The hourly output power of PV system is simulated considering solar irradiance， random change of weather， efficiency and effective sunlight area of PV arrays， efficiency of maximum power point tracking（MPPT） and inverter， and the reliability of overall PV system. The time-varying load model with randomness is incorporated in the probabilistic power flow and a program is developed. Case studies verify the feasibility and applicability of the method.