The leakage of natural gas is not only economic loss,also the fountain of dangerous. Optical sensors based on NIR tunable diode laser absorption spectroscopy were widely used because of high sensitivity,small volume and less maintenance. A portable remote sensor of natural gas pipeline leakage was reported with wavelength modulation and harmonic signals detection technology. With many materials as reflector used and field locale background simulated,the detection of gas leakage was preformed and better detection limit was got. The sensor is portable with only 5 kg weight.