We report a well-performing external phase lock system based on Mach-Zehnder interferometer (MZI) and optical phase lock loop (OPLL). The laser short-term frequency noise and phase noise is effectively suppressed by external phase lock system, which providing an extremely precise laser source for the quantum precision measurement system to inertial measurement such as atomic gyroscope. In addition, this system is independent of the laser for external control, which means that the system does not disturb the original operating conditions of laser. We carry out a theoretical analysis and experimental analysis for the external phase lock system, and design the parameters for MZI and OPLL based on theoretical analysis results. The linewidth of laser is narrowed from 500 kHz to 1.5 kHz after external phase lock. In addition, we effectively reduce the secondary peaks interference introduced in the transfer function nulls by introducing additional gain in the high frequency band. We measured the frequency fluctuation of the beat frequency signal, and the normalized Allan deviation decreased from \({1.114\times 10}^{-12}\) to \({1.178\times 10}^{-13}\) for a sample time of \({10}^{-1}s\) . The experiment confirms the superiority of external phase lock system in terms of short-term laser performance.