Abstract: The Space Environment Simulation and Research Infrastructure (SESRI) is a cluster accelerators designed to simulate various complex cosmic environments. Among them, the 300 MeV proton and heavy ion accelerator plays a crucial role in facilitating the study of the damaging effects of high-energy particle irradiation. The design, optimization and commissioning process of the SESRI synchrotron injection system is presented. During the design stage, particle simulations were carried out with the ACCSIM program. Subsequently, a multi-parameter optimization was performed using the Particle Swarm Optimization (PSO) algorithm, resulting in an optimized injection scheme characterized by enhanced accumulation gain and reduced emittance. In the device testing phase, measurements and corrections were conducted on the mechanical structure control parameters of the electrostatic septum, and optical parameters of the injection line, as well as the waveform tracking error of the bump magnets and power supplies. During the operational phase, the SESRI synchrotron successfully accumulated beam, achieving the injection design goals and validating the feasibility and stability of the injection system.