Based on the Off-axis Cavity Enhanced Absorption Spectroscopy (OA-CEAS) technique, a high sensitivity pollution gas detection system was made by using a tunable near infrared diode laser as light source and a high finesse optical cavity with two plan-concave mirrors of reflectivity of 97.97% as absorption cell. The absorption spectra of N2O gas mixtures centered at 6 561.39 cm-1 were obtained. The relationship between the absorption intensity and gaseous concentration was obtained by recording the absorption spectra of N2O gas mixtures at different concentration. The line-width of absorption spectroscopy vs the gas pressure and the detection limit was discussed as well. The minimum detection concentration was found to be 86 ppm using this cavity enhanced absorption spectroscopy system. Indicating the cavity enhanced absorption spectroscopy is a sensitive, easy manipulated, robust and simplified technique, which can be used for rapid gas analysis.