The invention relates to the technical field of acetylene cracking furnace production monitoring, and particularly discloses a CO laser detection system based on a thermal radiation background, which is used for solving the problem that an existing monitoring system is difficult to accurately distinguish CO and water vapor signals because thermal radiation and water vapor generated by high temperature in an existing ethylene cracking furnace interfere infrared absorption measurement of CO. Comprising a quantum cascade laser, a pyroelectric detector, a data processing unit and a signal analysis module, a reference light intensity adjusting module utilizes temperature, humidity and pressure data obtained by an environment parameter sensing module in real time to adjust the CO absorption coefficient through an environment correction factor, the reference light intensity is dynamically calculated and corrected according to the reference light intensity, and the signal analysis module analyzes the signal. The data processing unit is used for dynamic correction of CO concentration monitoring; a CO signal is effectively extracted under a thermal radiation background through a quantum cascade laser and a light beam modulation technology, environment correction and real-time monitoring are combined, CO concentration abnormity is accurately recognized, early warning is given out, and the monitoring sensitivity and reliability are improved.