Tunable diode laser absorption spectroscopic(TDLAS)technology applies the wavelength tunable characteristics of diode lasers to gain the absorption spectroscopy of the selected absorption line of the target gas for the qualitative and／or quantitative analysis of the pollution gases in air．In order to get the required sensitivity in trace gas monitoring and gas leak detection，based on the idiographic requirements it generally needs to adopt diferent laser modulation techniques like wavelength m odulation amplitude m odulation ． frequency or phase modulation and so on，with combination of long path absorption cell and assistance of various noise suppression techniques．TDLAS has significant advantages not only in sensitivity and high selectivity but also in rapidity of response．It has been extensively utilized in monitoring of various pollution gases in troposphere and atm osphere． and also in location the source of toxic or hazardous gas leak．W e report a TDLAS—based instrument recently developed bv our group for the measurement of CH4 in atmosphere． This instrument possesses advantages of fast response(faster than few millisecond)and low detection limitation f<100 ppbv1，and it could be easily assembled to a portable gas monitor． Furthermore，if the laser wavelength could be tuned in covering the range of 1．3一1．8“m or installing few narrow DFB tunable lasers to cover the range of 1．3一1．8 m，simultaneous monitoring of the major atmospheric pollution gases inchlding CO2、CH4、CO、CH2O、H2S、NH3、HCI、C2H2 and s0 on could be realized．