The invention discloses a device and a method for real-timely monitoring the signal conversion of a servo motor control system, wherein an isolating circuit of a high speed photoelectric coupler digitally isolates a clock signal of a single peripheral interface (SPI) bus, a data signal and an SPI selective signal from equipment, a complicated programmable logic device receives the data bits which are isolated by the high speed photoelectric coupler and combines every 16 data bits into a data byte, and the data byte is sent to a data buffer area in a universal serial bus (USB) device controller; a circuit of the USB device controller sends the data in the data buffer area to a computer; and an electrically erasable programmable read-only memory downloads the USB equipment controller code which is stored in the electrically erasable programmable read-only memory into the USB equipment controller. The transmission rate between a digital signal controller and a computer can be obviously improved, the working state of a servo motor is more intuitively reflected, and the real-time monitoring of the servo motor control system is realized.