The invention provides a millisecond grade real-time computer system monitoring device which can judge the running status of a real-time control computer within time in millisecond grade, give alarm and carry out protection in case of abnormality of the computer system, and enable the real-time control system to operate more safely. The invention comprises a standard time clock square wave generating circuit, a waveform frequency sorting circuit, a shift circuit, a latch circuit and a system running heartbeat signal detection circuit for detecting operation of the real-time computer system, wherein the standard time clock square wave generating circuit is connected with the waveform frequency sorting circuit which is connected with a shift register, the shift register is connected with the latch circuit, the real-time computer system detection circuit is connected with the shift register, and the latch circuit is also connected with a six freedom degrees motion simulator protection loop. The invention can be applicable to detect normal operating status of the real-time computer system and drive a protective device to carry out protection in case of system abnormality.