With the rapid development of high-speed railway (HSR), the contradiction between user service demand and available resource is increasing. Users have growing demands for fast, reliable network connectivity and efficient service experiences that are difficult to meet with traditional network architectures. Mobile edge computing (MEC) not only reduces delay but also ensures an efficient user experience by pushing rich computation and communication resource to the network edge. In this paper, we design an MEC framework for multi-user system in HSR scenario for solving the problem of joint optimization of computation offloading and resource allocation in system network. Our goal is to optimize the allocation of bandwidth and computation resource through real-time distance information to minimize the system cost. We propose an optimization algorithm based on an improved sparrow search algorithm (ISSA), which optimizes offloading decisions and rationalizes the allocation of system bandwidth resource and computation resource. Simulation results show that ISSA can efficiently decrease the consumption of computation and communication resource which improves the efficiency and performance of the system.