The input impedance of a constant power load usually behaves as negative incremental impedance characteristic, which may have strong impact on the system stability when it is interacting with the front-end converter in a microgrid.In this paper, an improved sliding mode control (SMC) method is proposed to improve the large signal stability of micro grid system.Firstly, the system uncertainties and external disturbances are considered in the system modeling, which make the control have strong robustness.Then, the adaptive algorithm is introduced in the sliding mode control to estimate the upper bound of the total disturbance, which improves the control accuracy.Finally, a simulation model of a microgrid is established in Matlab/Simulink.The effectiveness of the proposed method is verified by simulation results.