The invention discloses an automatic protection function verifying method for a microcomputer type main transformer differential protection device. On the basis of existing microcomputer type main transformer differential protection, the constant value area of the device and the external pressing plate input are read, and the protection function verifying item is determined according to the set protection input and output situations. A test scheme is automatically generated according to the set constant value, the alternating current secondary value and the voltage secondary value simulating the external fault information are assigned to the corresponding interior variables, and therefore the fault situation can be simulated. The input is changed till the protection action is achieved according to the test scheme, the testing process is recorded, the action value is analyzed, and therefore the test on one item of protection function is achieved. According to the automatic protection function verifying method for the microcomputer type main transformer differential protection device, additional hardware expenditure and outside loop wiring are not needed, the test on various protection functions of the whole set of device can be finished without manual intervention or protection test instrument, the testing process and result can be dynamically displayed, and the test report can be automatically generated.