Abstract: In the grid-connected mode, when grid frequency deviation occurs or dispatch command varies the output active power from virtual synchronous generator (abbr. VSG) fluctuates, however, existing VSG analysis and control mode can only response to the active power fluctuation caused by the change of dispatch command; when grid frequency deviation occurs, existing control strategy might lead to the larger fluctuation of VSG output active power. In allusion to above mentioned problem, firstly, the influence of VSG parameters on VSG dynamic performance under the grid frequency deviation and the relation between angle oscillation and virtual inertia under the variation of dispatch command were analyzed. Secondly, on this basis, a control strategy for virtual inertia was proposed, that is, when the variation of dispatch command occurred, the adaptive control of virtual inertia was adopted, and the principle for the parameter selection was given. Thirdly, when grid frequency deviation occurred, the information entropy-based optimizing value of virtual inertia was adopted. Finally, by means of Matlab/Simulink simulation, the superior dynamic performance of the proposed virtual inertia control strategy under the deviation of active power dispatch and grid frequency deviation was verified.