Abstract: A multi-computer (KVM) switcher with ability to extend universal serial bus (USB) host interface via serial peripheral interface (SPI), characterized in that SPI master device interface of master control unit can switch the capability of controlling plural SPI slave devices via serial peripheral interface (SPI), and through installing SPI slave device interfaces on plural universal serial bus (USB) host interface control units to be extended, the object of extending peripheral device with USB interface via SPI interface is achieved.