Tunable diode laser absorption spectroscopy (TDLAS) is a highly sensitive, highly selective, noninvasive and real-time trace gas detection technique, which has been widely used in atmospheric monitoring and industrial control. In the present research, a new type of widely tunable SG-DBR diode laser (WTDL) with a tunable range of about 1 520~1 570 nm was use as the light source for tunable diode laser absorption spectroscopy combined with the wavelength modulation (wm) to measure the spectrum of multi-gases. Also the structure, performance and other characteristics of WTDL were introduced. There were 18 channels compiled to the SG-DBR laser, which emitted central wavelength at the optimum absorption transitions of CO, CO2 and H2O by homemade program, of which 14 channels (corresponding to absorption lines of CO and CO2) were investigated by second harmonic detection technique. Meanwhile, the detectabilities in these channel were analyzed which are about 10-5 at the peak absorbance. The experiment results validate the feasibility of SG-DBR laser used as light source in multi-gases detection using wavelength modulation absorption spectroscopy technique in practical application. That could effectively reduce the cost and complexity of system in the field of TDLAS technique.