For the problem of low capacity penetration caused by over voltage, over voltage during the operation of islanded DG, and the transient over voltage between transition of DG both from islanded operation mode to grid-connected operation mode when photovoltaic DGs access to distribution network, this paper puts forward a kind of P/U droop control method, which can avoid photovoltaic DG exiting operation due to over voltage when it accesses to distribution network. When the load is reduced, the DG power increases and other factors causing over voltage in islanded DG including photovoltaic DG, the method can achieve the steady energy balance of islanded MG without control interconnections and also can solve the transient over voltage between transition of MG both from islanded mode to grid-connected mode. Firstly, the voltage deviation formula is given and over voltage generation mechanism is analyzed. Secondly, the P-U regulating method is introduced. And then in order to verify the feasibility of the method, taking photovoltaic DG accessing to distribution network as the object of analysis, the Matlab/Simulink simulation model and experiment are presented from the platform of photovoltaic inverter. The results show that P/U droop control method is effective.