When the LCL filter was used in the Photovoltaic (PV) grid connected system, the mathematical model of the system had high order, the design of conventional backstepping method would be encountered with the problem of the multiple virtual control volumes gradually derivation, which not only had complicated calculation, but also would increase the measurement noise, and lead to increase the current error and harmonic of the output current. In order to solve the problem, the paper designed a photovoltaic grid connected system based on filtering backstepping method. The method was combined with the Lyapunov stability theory and implemented the derivation of virtual control volumes by a filter. It has reduced the measurement noise significantly. The theoretical analysis and the simulation results show that, current error and output current total harmonic distortion (THD) of the method is small. The method can achieve good grid synchronization performance and has a good practical value.