SPI (Serial Peripheral Interface) is a full-duplex serial communication interface bus. Now, many devices adopt SPI. However, in many other aspects, microcontroller and microprocessor have no SPI interface, data transmission is inconvenient. With the development of FPGA technology, the problem can be solved absolutely by the I/O port of FPGA. In this paper, after introducing the principle of SPI, we designed SPI interface with FPGA and implemented the communication between SPI interface and the device of CRG20 which has a SPI interface. The algorithm of design SPI interface through FPGA is implemented with VHDL. The results of simulation in Quartus II and FPGA simulation are also described. The SPI bus interface modules fulfill the goal demanded.