To solve the problem of poor communication performance of traditional multi-user dual-function radar communication system due to carrier allocation and improve the resource utilization rate of dual-function radar communication system, a multi-user power allocation scheme based on the communication user carrier sharing model is proposed, and the system has better communication performance by constructing a reasonable resource allocation problem. Firstly, the model of communication user carrier sharing signal in dual-function radar communication system is established. Secondly, in order to ensure the performance of the dual-function radar communication system, an optimization problem is constructed to maximize the system communication and rate and satisfy the constraints of radar signal-to-noise ratio lower bound, total power and user power. The feasibility of the optimization problem is strictly proved through theoretical analysis. Finally, in order to solve the convex optimization problem, a multi-user power allocation algorithm is proposed, which firstly introduces auxiliary variables to convert the objective function twice, decomposes it into two optimization sub-problems, which are then solved by alternate iteration. The results show that compared with the traditional user carrier allocation model, the communication rate of the optimized user carrier sharing model are increased by about 40%, which verifies that the proposed scheme has better communication performance and effectively improves the utilization rate of system resources. The research results of this paper provide a new idea and means for improving the communication performance of multi-user dual-function radar communication system.