A gas sensor absorption cell was introduced which was made of two corner cube prisms. The stability and sensitivity of the cell were improved using the reflectivity character and the senseless to tilting of light beam. The transmission characteristics of light beam were analyzed with geometric optics. Moreover, the transmission equation of probing light and the measurement equation of the system at both single-wavelength and dual-wavelength were put forward , and a gas concentration detection system was constructed. It is concluded that the times N of probing light traveling back and forth in the cell is determined by the distance between axes of the two corner cube prisms, the sensitivity for differential optical absorption spectroscopy(DOAS) is proportional to the times N. The sensor was used to detect concentration of methane.The results show that the inspection threshold of the cell approaches 50 ppm for methane at N is 3.