Aiming at the deviation of the parallelism(on to one correspondence position) between the active laser field of view and the infrared passive field of view in the parallelism correction of the active and passive dual-band (laser/IR) composite system, the parallelism correction method of the active and passive dual-band (laser/IR) composite system was proposed and the theoretical research and physical simulation test were carried out. First, derived the angle correspondence between the active laser emission field of view and the fast steering mirror. Secondly, a parallelism correction method based on polynomial fitting is proposed according to the laser emission field of view and infrared detection field of view. Finally, the actual test platform is constructed to calibrate, solve and correct. The test results showed that the actual maximum deviation can be reduced from 0.8 mrad to less than 0.1 mrad in the ±1.4° indicated field of view of laser and ±1.4° infrared central field of view, which further improve the aiming accuracy of the laser.