The integrated technology of precision ranging and high-speed communication has developed into one of the main research direction of inter-satellite laser links. In order to explore the influence mechanism of the communication demodulation algorithm based on the space laser communication system on the ranging performance, according to the existing laser communication system architecture, this paper analyzes the working principle of the integrated system of ranging and communication, and builds a laser based on symbol synchronization. Based on the integrated system model of ranging and communication, the ranging accuracy of the signal tracking system based on Gardner synchronous loop is analyzed, and the phase detection algorithm is optimized. Theory and simulation prove that the optimized symbol synchronization loop can realize symbol synchronization judgment and distance calculation at the same time, and obtain a 4 dB noise tolerance improvement. The ranging variance is mainly related to baseband shaping filter parameters, loop bandwidth, carrier noise. It is related to factors such as ratio and phase detection gain. The algorithm is simple, not affected by the carrier phase, has good compatibility with high-order modulation, and is suitable for space laser link systems. The system model and algorithm proposed in this paper enrich the theory of ranging and communication integration, and provide simulation basis for the subsequent integrated system design.