In order to solve the problem of user's fairness in D2D (Device-to-Device) communication system, firstly, the existing proportional fairness principle was extended to derive an optimization problem relating to weighted sum-rate, and then a KMPF (Kuhn-Munkras Proportional Fair) resource allocation algorithm was proposed to optimize it. The algorithm maximized the user's weighted sum-rate through power control, and allocated the cellular user's resources that could be reused for the D2D users according to maximization of the total weighted sum-rate by Kuhn-Munkras (KM) algorithm. Simulation results show that the fairness index of the proposed algorithm is 0.4 higher than that of the greedy resource allocation algorithm and the throughput of the system is over 95% of its level, and the throughput of proposed algorithm is about 50% higher than that of the random resource allocation algorithms. It is shown that the algorithm can solve the problem of user's fairness while considering the system throughput.