It is difficult to control dual-mode smooth switch for grid-connected and off-grid photovoltaic power generation system. Establish simulation model of three phase photovoltaic power generation system, analysis and research switching control strategies of grid-connected and off-grid model for photovoltaic inverter. A method to realize smooth switch between grid-connected and off–grid was proposed. Three split-phase switches were used to operate switch by detecting zero grid voltage of each phase and coordinating transformation sequence of control strategy reasonably. PI controller was used to make load initial value to maintain voltage stability. Result of simulation display that inverter’s waveform were improved effectively and prove the feasibility of the control scheme.