Magnetic effects in the laser gyro application process can cause a change of the bias stability of gyro, which will have a major impact on gyro accuracy. The theoretical model about the magnetic effect of the laser gyro is established to analyze factors which generate the magnetic effect. Analyzing result shows that the little non-coplanar optical path in the laser gyro magnetic effects is the main reason of magnetic sensitivity. Magnetic effects of laser gyro can be decreased by adjusting the axial direction of a cavity pan mirror to reduce the optical path of non-coplanar angle. The above conclusions are proved by the experiment.