The invention discloses a RISC-V-based hybrid mixed computing system and method. The system comprises an instruction control module and a mixed calculation module, an expansion instruction is arrangedin the instruction control module, and the expansion instruction contains operation information; the instruction control module is used for automatically setting operation data and operation information in sequence and then transmitting the operation data and the operation information to the hybrid mixed calculation module through an extension instruction; and the hybrid calculation module is used for selecting a corresponding operation mode according to the operation information, performing hybrid operation by combining the operation data and the selected operation mode, and outputting an operation result. Complex hybrid operation is achieved through a single extension instruction, and some complex operations of the processor based on the RISC-V instruction set are simplified. The calculation process of complex hybrid computation is simplified; the disassembling machine code is simpler and clearer; time consumption caused by multiple times of cyclic operation is reduced, the system performance is improved, and the method can be widely applied to the technical field of communication.