Abstract:  Considering the characteristics of the main controller of the digital control system (DCS) platform of security level and its function and application, based on the specifications in relevant laws, regulations and standards, studies had been conducted on the diagnosis, redundancy, communication and embedded design of the highly reliable main controller. Key technologies such as software development were studied and applied in the design of the main control module of the China National Nuclear Corporation's  DCS platform of security level, the Nuclear Advanced Safety Platform of I&C (NASPIC). At the same time, the HPR1000 simulation platform was built and its functions and performance were tested in the shutdown function test, engineering safety facility actuation function test and periodic tests. These tests and the qualification test conducted by the National Nuclear Safety Administration showed that the diagnostic coverage rate reached 98%, exceeding the standard requirements; the measured communication error rate was less than 10-11, meeting or even exceeding the security level DCS product specifications of other manufacturers; the hot standby redundancy architecture and embedded software meet the requirements of Class 1E equipment, ensuring the high reliability of the main controller.