A system identification method based on LS and GA was proposed, and applied to the test of viscous damping coefficient of spool valve.A test system of the viscous damping coefficient of spool valve was built. According to experimental data,the system parameters were identified by RLS algorithm, getting the range of solution space.Then the improved adaptive genetic algorithm was used for accurate identification. Finally, the viscous damping coefficient of the spool valve was obtained. The identification results of viscous damping coefficient were analyzed.It is shown that the identification data are in good agreement with the real experimental data, the effectiveness of the proposed method is proved.