A LCL filter is adopted as an interface between grid-connected inverter and power grid. The mathematical model of the LCL filter is built, and then a control method for grid-connected inverter with a LCL filter is proposed. This control method employs an external grid-side current loop and an internal inverter-side current loop. And this control method can not only protect power switches effectively, but also ensure the system stability and high in-grid power factor. Based on the Hurwitz stability criterion and Lienard Chipart stability criterion, the design method of controller parameters in inner and outer loops is derived. Simulations and experiments of grid-connected inverter in grid-connected mode are conducted. Simulation and experimental results validate the correctness and feasibility of the proposed method. This work is supported by National Natural Science Foundation of China (No. 51207156).