Abstract: A CO concentration analysis system for natural gas was developed based on the diffuse absorption band of CO gas molecules at 1.56 m, combined with wavelength modulation and harmonic detection techniques. A long light path gas absorption cell was used to analyze CO concentration. The system was mainly composed of laser driving module (voltage-controlled constant current source and temperature control circuit) gas chamber of gas absorption cell and phase-locked amplifying circuit and other signal processing modules. A hybrid simulated gas station developed by the laboratory was used to simulate the natural gas background with different standard concentrations of CO gas. The experimental results show that the minimum detection limit of the system is up to 5.6 ppm; the relative error of CO gas with 0.05% concentration is less than 2; and the relative error is less than 1.8% for standard CO gas with 10% concentration. When the range of CO concentration is 0-100 ppm, the detection sensitivity is 0.09 mV/ppm. Compared with the CO detection system of the quantum cascade laser, the system has the advantages of high performance-to-price ratio, suitable for complex oil and gas development, and has great application value in the field of petroleum, chemical and natural gas.