For the power system with a large number of power electronic equipment, it is difficult for the traditional electromagnetic transient real-time simulator to realize the small step length simulation. To solve this problem, a hybrid step length real-time simulation method based on field programmable gate array (FPGA) and CPU is adopted to build a transient real-time simulator for power system. Taking photovoltaic power generation system as an example, the system is divided into large step part and small step part by model segmentation method, and asynchronous communication between FPGA and CPU is realized through Ethernet, forming a large step length and small step length hybrid co-simulation platform. Aiming at the error caused by system data interaction after model segmentation, a pulse equivalent averaging method is proposed to equivalent the output voltage of inverter at AC side, so as to reduce the error and FPGA hardware resource occupancy rate. Finally, the real-time simulation results are compared with the simulation results of Simulink offline model and the model before optimization, and it is verified that the proposed method has certain advantages in reducing the resource occupancy under the premise of ensuring the simulation accuracy.