In electronics, a multiplexer is a device that performs multiplexing; it selects one of many analog or digital input signals and forwards the selected input into a single line. In this paper, we propose a design method for multiplexer design in the environment of single-cycle CPU system based on the MIPS instruction set, and the software Schematic and VHDL is introduced in order to speed up the development cycle. Furthermore, we discuss the consideration and operational principle of design and realization in detail. The simulation results for the part constructed by FPGA are also presented.