The magnetic effect is one of the important error sources that limits the precision of four frequency differential laser gyro. Physical mechanism is analyzed from the operational principle of differential laser gyro, then a novel method of decreasing the magnetic effect is presented. Based on the concept of light intensity difference frequency stabilization, the most suitable frequency stabilization point can be chosen by changing the judging standard of frequency stabilization. At the same time, some pertinent measures are adopted to ensure the stability of the gyro parameters especially the total light intensity. The validity of this method is verified by the experiment results.