［Objective］The existing 40.5 kV AC comprehensive protection device of urban rail transit (hereinafter referred to as AC CPD) relies on imported system-level chips, which greatly restrict the localization of equipment, so it is urgent to localize the software and hardware development of AC CPD.［Method］The structure and function of the existing 40.5 kV AC CPD equipped with system-level imported chips are briefly described. Based on the localization requirements of 40.5 kV AC CPD in China′s urban rail transit, a domestic chip design scheme with dual FPGA (field programmable gate array) integration based on SPI (serial peripheral interface) bus expansion technology is proposed. The hardware electromagnetic compatibility test, software protection function test, and performance test in high temperature and high humidity environment are carried out on the localized AC CPD equipped with domestic chips, and the main performance indicators of the localized and the existing AC CPD are compared. Finally, the application of the localized AC CPD adopted in urban rail transit engineering is briefly described.［Result & Conclusion］The test results of hardware electromagnetic compatibility and software protection function for the localized AC CPD meet the requirements of the State Grid, and its main performance level is equivalent to that of the existing AC CPD. The device is stable and reliable in the application project, and the performance is excellent. The application of this device can effectively solve the problems of incomplete categories, limited performance, and insufficient interface of some domestic devices, and fundamentally solve the problem of relay protection key components and software operating systems heavily dependent on imported equipment.