The invention provides a source code coverage rate test method and system based on an RISC-V extension instruction, and the method comprises the steps: carrying out the syntax tree analysis of a source code, obtaining an instrumentation point, and defining the instrumentation point as a set position; slicing the source code according to the syntax structure of the source code, and performing instrumentation at a set position, the instrumentation statement of the instrumentation being an RISC-V-based extension instruction; executing the source code, and performing data acquisition on the outputof the extension instruction to obtain instrumentation output information; and analyzing to obtain a source code coverage rate test result according to the instrumentation statement and the instrumentation output information. By expanding the RISC-V instruction, external high-speed data sending inside the CPU is achieved, and compared with an asynchronous bus, the number of pins is greatly reduced. A tested board card does not need to fly, so that the workload is greatly reduced.