The embodiment of the invention provides a method and device for predicting grid-connected transient stability of a virtual synchronous generator. The method comprises the following steps of acquiringthe virtual rotating speed and a virtual power angle of a virtual synchronous generator VSG; inputting the virtual rotating speed and the virtual power angle into a preset transient energy function model, and outputting a transient energy value and the critical clearing time; and predicting the grid-connected transient stability of the VSG according to the transient energy value and the criticalclearing time. According to the method and the device for predicting the grid-connected transient stability of the virtual synchronous generator provided by the invention, a transient energy functionof a one-machine infinite system connected to the VSG is constructed, and the effect of virtual damping is taken into account; the established transient energy function is high in accuracy, the grid-connected transient stability of the virtual synchronous generator is predicted by calculating the transient energy function, the calculation amount is small, the use is convenient, and the predictionefficiency is high.