Acqusition, pointing and tracking is the key technology in space laser communication system. And it is the premise of the communication link establishment. The initial alignment as the first step in the acquisition system is the decisive factor for the success of the acquisition, the acquisition probability, and the length of time. To quickly establish the space laser communication link, the initial alignment system model is established by analyzing the composition and working principle of the initial alignment technique. Calibration method on initial alignment lineofsight is proposed, and the system alignment accuracy is obtained according to error analysis method. The experimental results show that the alignment system can quickly establish the space laser communication link, and it has high alignment accuracy, which verifies the correctness and feasibility of the alignment system.