Abstract: Since the pure digital simulation software cannot realistically simulate the response characteristics of the control and protection device of the flexible HVDC transmission system, there is some errors if it is used to check the overall function of the control and protection device, optimize and verify the control and protection parameters. A hardware in the loop (HIL) simulation platform based on RT-LAB is established in this paper. The data merge is realized by the high-speed protocol conversion control chassis to meet the high speed requirement of communication interface. In view of the performance of the control and protection device, a test scheme of converter station control and basic valve controller is designed, and the relevant tests are completed based on the built platform. The dynamic performance test and the function test verify the validity of the MMC hardware in the loop simulation platform and the rationality of the test scheme, which can meet requirements of the control and protection device performance testing.