A cavity-enhanced absorption spectroscopy (CEAS) system has been build up, in the system, a tunable near-infrared DFB diode laser is used as the light source, and an optical cavity which is consisted of two mirrors with reflectivity of 99.7% is used as the absorption cell. Based on the working condition of the diode laser and optical cavity, the technology of CEAS is divided into three kinds: control wavelength CEAS, control cavity length CEAS and both scan wavelength & cavity length CEAS. Carbon dioxide (CO2) and methane (CH4) is used as the main sample gas, control wavelength CEAS and control cavity length CEAS are used to get the absorption spectroscopy of CO2 near the region of 1.573 μm; both scan wavelength & cavity length CEAS are used to get the absorption spectroscopy of CH4 near the region of 1.316 μm, the sensivity and the quantitative analytical ability of the three CEAS is also studied. It demonstrates that CEAS is a quantitative absorption spectroscopy technologic with the advantage of simple setup, easy operation, high sensivity and good stability; the sensivity of both scan wavelength and cavity length CEAS is superior to 1.15×10-7 cm-1.