In this paper, CFBR-II fast neutron reactor (China's second fast neutron pulse reactor) and Co-60 device are used to carry out experiments on different sequential neutrons/gamma irradiated bipolar transistors. Under the condition that the collector-emitter voltage is constant, the variation curve of the bipolar transistor current gain with the collector current is measured, and the influence of different irradiation order of neutron/ gamma on the current gain of the bipolar transistor is studied. The experimental results show that when the collector-emitter voltage is constant and the collector current is extremely low, the current gain degradation of the bipolar transistor is relatively large, and the current gain increases with the collector current. The degradation of the current gain of the bipolar transistor caused by the gamma irradiation after the neutron pre-irradiation would be greater than that of the neutron irradiation after the gamma pre-irradiation, and the difference is more obvious in PNP transistor than in NPN transistor. This paper presents a preliminary discussion on the related mechanism.