The invention discloses a microprocessor system bus and MPI bus conversion device and method, which realize the data communication between the microprocessor system bus and peripheral device MPI bus. In the device, a control signal processing module is used to receive control signals sent by the control bus, when the read operation signal or write operation signal in the control signal is effective, the chip select signal on the MPI bus is made to be effective; a read-write operation module is used to receive and store the first paralleling data transmitted by the data bus when the write operation signal is effective, and to transmit the stored second paralleling data onto the data bus when the read operation signal is effective; a paralleling and serial data conversion module is used to transmit the first paralleling data bit-by-bit in sequence onto the MPI bus when the write operation signal is effective, and to receive a set of serial data with the same bit of the data bus from the MPI bus and stores in the read-write operation module bit-by-bit in sequence to form a second paralleling data when the read operation signal is effective.