The virtual synchronous generator (VSG) has been widely concerned because of imitating the voltage and frequency regulation characteristics and inertial damping of synchronous generator(SG). The traditional VSG characteristic analysis generally aims at the condition that the grid frequency is rated frequency, when the grid frequency is not equal to the rated frequency, the traditional VSG control will change the dynamic characteristics of VSG and lead to the deviation of the output active power steady-state value, The existing literatures pay no attention to the analysis of the dynamic characteristics of VSG under the grid frequency deviation and the existing scheme can not completely solve the power deviation problem. Firstly, the influence of grid frequency deviation on the active power and frequency characteristic of VSG was analyzed in this paper, then an improved active power control strategy was proposed and analyzed. Lastly, the effectiveness of the proposed control strategy was verified by matlab/simulink simulation.