Abstract: In the process of working, the measured Gamma spectrum of in situ seawater Gamma spectrometer based on NaI(Tl) scintillation crystal detection method is prone to drift under the influence of ambient temperature changes, which brings difficulties to the radionuclides’ activity analysis. At present, spectrum stabilization methods for terrestrial environmental Gamma spectrometer usually introduce radioactive reference sources,which are not suitable for the measurement of low-level radioactive environment in seawater. In this paper, experiments are designed to study the rule of temperature drift of Gamma spectrum. It is found that the proportion of peak channel address drift with temperature of different characteristic peaks is basically the same, and the trend of peak channel address change with temperature is the same, and there are inflection points. When the peak channel address is lower than 15 ℃, it increases with the increase of temperature, while when it is higher than 15 ℃, it decreases with the increase of temperature. According to the study of the relationship between the gain and the peak channel address of the in situ seawater Gamma-ray spectrometer, a spectrum stabilization method based on the natural characteristic peak of radionuclides in seawater is proposed. The experimental results show that the Gamma-ray spectrum obtained by using the spectral stabilization method have good coincidence under different temperature conditions, and the maximum drift channel number of peak channel address is −1-+1 channel. This method can effectively stabilize the temperature drift of the in situ seawater Gamma spectrometer and meet the requirements of the long-term automatic operation for Gamma spectroscopy measurements in seawater.