In order to achieve the HVDC control and protection system safe and reliable interlocking function, based on the field level device application scenarios in-depth study, this paper proposes a new measurement & control device software architecture and design method. The basic measurement & control functions and logic interlock function to be the second programmed are separated from one another, system periodic calls are used to achieve the integration of logic interlock program and measurement & control basic programs. The method is based on low-cost hardware and software platform, its measurement & control device used is based on Infineon C167 microprocessor, the standard IEC61131 graphical design language is adopted, and the program design is simple and highly reliable, not dependent on specific hardware, and suitable for implementing on different hardware platforms. The experimental data of Guanyinyan HVDC Project shows that the software control strategy has a low maintenance cost, high reliability and easy migration characteristics, and it has an important application value for control and protection system to achieve safe and reliable interlock function.