Abstract: The photovoltaic power generation system would generate the voltage fluctuation and the harmonic since it can be easily affected by external conditions and traditional maximum power point tracking can not balance the problems of tracking velocity and steady state oscillation. in this paper, variable endpoint optimal trajectory is used to track Maximum power point of Three-phase Photovoltaic Grid Connected System by constructing elecric power function and voltage target line function. And then extremum condition is used to optimal trajectory of the voltage. At last, the output voltage must track the optimal trajectory voltage by Model Reference Adaptive System. In Model Reference Adaptive System, the optimal trajectory voltage is the output of the reference model. Finally, the output voltage of the object can fully track the optimal trajectory voltage. At last the simulation shows that the ideal effect, the faster dynamic response speed, the smaller steady-state error and the good dynamic, static performance of the object.