In order to reduce magnetic sensitivity of four-frequency differential laser gyro (DILAG),effect of operating point on magnetic sensitivity was investigated.According to theoretical analysis,magnetic sensitivity arises mainly from unequal relative scale factor corrections of left and right circularly polarized gyros.The DILAG,however,is insensitive to magnetic field when operating at the optimal point.Axial magnetic filed was produced by winding coil around gain tube,and operating point was changed by adjusting voltage of piezoelectric transducer affixed to cavity mirror in our experiment.As a result,the curve of magnetic sensitivity versus operating point was obtained.The results showed that DILAG was insensitive to magnetic field at the optimal operating point,which uniquely existed within operating area.Environmental disturbance would be reduced when DILAG was operating at the optimal point.This helped to improve DILAG performance.The conventional frequency stabilization method using light intensity comparison should be changed so as to make sure DILAG operating at the optimal point.