A mid-infrared carbon dioxide (CO₂) sensor is presented for the application in greenhouse environment. An integrated multi-pass gas chamber and a dual-channel differential detection method are adopted to decrease response time and suppress environmental influence, respectively. An optical module is developed using a cost-effective wideband mid-infrared light source, a dual-channel pyre electrical detector and a spherical mirror, and the moisture-proof function is specially designed for enabling the application of this sensor in greenhouse with high humidity. Experiments are carried out to evaluate the sensing performance on CO₂concentration. According to the experimental results, the limit of detection (LoD) is about 3×10^{-5with an absorption length of 30 cm. The relative detection error is less than 5% within the measurement range of 3×10-5—5×10-3. Based on 10 h long-term stability measurement on 5×10-4and 2×10-3standard CO2 samples, the maximum fluctuations are 1.08% and 3.6%, respectively. By using a 2.4 GHz wireless network communication system for remote monitoring and data recording, a field measurement of this sensor in a greenhouse is conducted, and good performance is proven in such circumstance.}