Portable corrosive gas micro water laser analyzer adopts TDLAS second harmonic principle to detect the micro water content in corrosive gas. The laser beam output by the modulated light source is led out by optical fiber and passes through the long optical path gas absorption pool. Since the electrical signal of the optical path is extremely weak after being converted by the photodetector, it also needs to be amplified by a preamplifier. The second harmonic signal is extracted by a lock-in amplifier with frequency doubling 2f as the reference signal. The second harmonic signal contains the information of gas concentration to be measured, and the data is processed after analog-digital conversion, and then the gas concentration to be measured is inverted by Lambert-Beer law. The product analysis accuracy is high, the reaction speed is fast, and the traditional method is overcome with large drift. The disadvantage of being susceptible to background gases such as H2.O2.