In the optical part of a fire control system, the parallelism of the laser and infrared units is a key factor that affects the performance of the system. As the targets are usually tracked with the infrared image, the laser unit′s operation range would degrade dramatically if the laser′s axis of sight deviates from the infrareds′.A reliable and flexible adjusting mechanism is presented in this paper. Optimum design, improved art and craft are utilized in the development, it comes out that multi axis are precisely collimated And the structure is robust against the mobilization, vibration and shock. It is shown that the aiming device has good reliability and stability, which contributes much to the high accuracy of the optical system.