According to the latest regulation for grid-connected photovoltaic system, a new operating control strategy for inverter low voltage ride through is presented in this paper. When the system happened to serious faults, the reactive current outputed priority as large as possible, in order to provide the grid larger reactive power support. When slight fault occurs to system, photovoltaic power can output maximum active power, and it can provide enough reactive power support at the same time. On this basis, a controlled current source model of the photovoltaic power station which is controlled by grid-connected joint voltage and timely maximum active power is established.This paper proposes an accurate theoretical analysis and method for grid fault when it is connected with large scale photovoltaic power stations, and then power fault equation and its solution method are introduced. Finally, the example calculation and simulation design verify the feasibility and correctness of the theoretical analysis.