Abstract: The population pulsation effect in the gain medium was considered to research the fine mode coupling effects in the laser gyro. Proceeding from the laser physics principle, the generation mechanism of population pulsation is analyzed. In association with the characteristics of four-frequency differential laser gyro, it is found that the population pulsation effect is one of the fine mode coupling effects. The level of the population pulsation effect in the coupling effects was calculated numerically. The result shows that the variation of the population pulsation effect with the cavity tuning is basically in accordance with other coupling effects, and it has small value in large cavity tuning ranges, which is less than 4% of other coupling effects; but it has relatively large value in some cavity tuning ranges (0.37＜＜0.46, 0.02＜＜0.06, 0.86＜＜0.88), which is more than 80% of other coupling effects. Therefore, it cant be ignored in the mode coupling analysis of the laser gyro.