A differential carbon monoxide (CO) concentration sensing device using a self-fabricated spherical mirror (e.g. light-collector) and a multi-pass gas-chamber is presented in this paper. Single-source dual-channel detection method is adopted to suppress the interferences from light source, optical path and environmental changes. Detection principle of the device is described, and both the optical part and the electrical part are developed. Experiments are carried out to evaluate the sensing performance on CO concentration. The results indicate that at 1.013×10⁵Pa and 298 K, the limit of detection (LoD) is about 11.5 mg/m³ with an absorption length of 40 cm. As the gas concentration gets larger than 115 mg/m³(1.013×10⁵Pa, 298 K), the relative detection error falls into the range of -1.7%—+1.9%. Based on 12 h long-term measurement on the 115 mg/m³and 1 150 mg/m³CO samples, the maximum detection errors are about 0.9% and 5.5%, respectively. Due to the low cost and competitive characteristics, the proposed device shows potential applications in CO detection in the circumstances of coal-mine production and environmental protection.