The synchronization accuracy of the electronic gearbox of the gear grinding machine directly affects the machining accuracy of the gear grinding machine. In order to fill the blank of the synchronization accuracy inspection of the electronic gearbox of the gear grinding machine, this paper proposes a synchronization accuracy inspection method of the electronic gearbox of the gear grinding machine based on the principle of continuous spreading machining. Firstly the method analyzes the influence of each axis following error on each precision of the machined gear by establishing the geometric model of worm wheel and machined gear, and then derive the formula for predicting each accuracy class of the machined gear by following error in each axis. According to the established mapping relationship of Following Error - Toth Surface Deviation, then combined with the formula for calculating the tolerance value of each precision of the gear, deduces the tolerance value of the electronic gearbox following error of the gear grinding machine. Finally, base on the established mapping relationship between following error and tooth surface deviation, combined with the formula for calculating the tolerance values of each precision of gears, deduce the formula for calculating the tolerance value of following error of electronic gearboxes and the tolerance values allow the synchronization precision of electronic gearboxes of gear grinding machines to be examined and evaluated. Compared with the previous grinding machine transmission accuracy inspection methods, this method is more applicable to the CNC gear grinding machine tools that use electronic gearboxes to control the movement of each axis. This study not only broadens the inspection scope of the old standard, but also provides an inspection idea and theoretical basis for the synchronization accuracy of electronic gearboxes of new CNC gear grinding machine tools.