Continuous wave cavity ring-down spectroscopy (CW-CRDS) can be utilized in high sensitive trace gas detection. Based on CW-CRDS, using near-infrared distributed feedback diode laser (DFB-DL), semiconductor optical amplifier (SOA), and self-designed high-finesse Fabry-Pérot cavity, laser driver and threshold detection circuit, the compact design of trace gas analyzer have been realized. In the system, SOA not only amplifies the laser power and improves the signal-to-noise ratio of ring-down signal, but also acts as an optical switch to trigger the ring-down time. The whole system is integrated in a 700 mm × 300 mm × 185 mm customized cabinet. Based on this device, CO2 gas is measured at 6359.97 cm-1, and the time series analysis results of the empty cavity ring-down time shows that the detection limit of the system is 3.85×10-8 cm-1.