Progressive gain is one of the important parameters for evaluating the performance of dynode photomultiplier tube (PMT), but there is only one related test system at home, which relies on manual operation and the test efficiency is not high. In order to improve the efficiency of testing progressive gain, an automatic test system for the progressive gain of dynode PMT was designed. The continuous adjustment of the light source output intensity was achieved by an automatic light system composed of controllable disphragm, electric baffle and etc, and the on-off of the progressive voltage was controlled by the high-voltage module, the voltage divider module and the relay module. Finally, based on the galvanometer module with an accuracy of 0.01 nA, the acquisition, processing and transmission of the signal was completed, so as to realize the automatic measurement of the progressive gain. The experimental results show that the proposed system can effectively measure the progressive gain characteristics of the dynode PMT, and the test repeatability is within 2%, which meets the test requirements.