Reducing the deviation of light path in cavity can improve mechanically dithered RLG vibration performance. The mechanism of the deviation of light path in the cavity of mechanically dithered RLG was analyzed and simulated. According to the results, the main reasons of light path deviation were dithered tangential inertial force and vibration impact inertial force. Meanwhile, the deviation of light path in cavity of RLG could change the RLG bias produced by Langmuir flow. The two main effective means of reducing Langmuir flow bias produced by vibration and improving gyro vibration performance were decreasing working current and improving stability of light path in cavity. The mechanism of mechanically dithered RLG light path deviation was validated by test. Compared with vibration test results of different working current, the vibration performance of RLG is improved obviously by reducing working current. The means of improving vibration performance by decreasing working current and increasing stability of light path is put forward, which is useful to improve vibration performance of mechanically dithered RLG and reform for the further development of RLG.