Bipolar devices are extremely sensitive to ionization effects, and their low dose rate radiation damage is more serious than their high dose rate radiation damage, which phenomenon is especially named enhanced low dose rate sensitivity. In the actual space radiation environment, the radiation dose rate of the device is extremely low. Currently, the enhanced low dose rate sensitivity effect has become a key factor of evaluating the reliability of spacecraft and its electronic systems, due to the fact that the low dose rate irradiation test needs longer time. The method to speed up the test on the ground is one of the hottest topics in this research area. In recent years, some researches have suggested that the use of hydrogen immersion irradiation for accelerating the test can simulate low dose rate radiation damage to some extent, but the damage mechanism has not been analyzed in detail. In this paper, the mechanisms of electrical properties and deep level defects for the 3DG111 transistor by ⁶⁰Co gamma ray under high and low dose rates in the cases with and without hydrogen are investigated. In order to analyze the damage mechanism of bipolar junction transistor, the excess base current and deep level transient spectrum are measured by using semiconductor parameter analyzer and deep level transient spectroscopy. The experimental results show that the current gain degradation of 3DG111 transistor is more serious under low dose rate radiation than under high dose rate radiation, at the same time, the excess base current of transistor increases significantly. This shows that in the device there appears the enhanced low dose rate sensitivity. Under both high dose rate radiation and low dose rate irradiation, the radiation damage defects are the traps for both oxide positive charge and interface state. Under the low dose rate irradiation, there are two main reasons for the increase in transistor damage. First, the oxide charge concentration increases under low dose rate irradiation, and the oxide charge and interface state energy levels move toward the middle band. Eventually, the space charge region recombination of the transistor is intensified, and thus causing the excessive base current of the transistor to increase and transistor performance to degrade. The comparison shows that the number and type of defects under the high dose rate irradiation are the same as those under the low dose rate irradiation. Based on the analysis, the hydrogen treatment can be used as an effective method of accelerating the assessment of radiation damage enhancement effect at low dose rates.