HCl gas is one of the waste incineration emissions. It does not only corrode the incineration equipment and monitoring instrument, but also harms human health. Effective online monitoring of the HCl gas concentration ensures normal use of the incineration equipment and function of the monitoring instrument. An online HCl concentration analyzer based on tunable diode laser absorption spectroscopy (TDLAS) is presented. The laboratory tests show that the linearity error of the analyzer is not higher than ±1% F.S and the stability of the analyzer is good. The analyzer has been successfully applied to the exhaust vent of a waste incineration equipment for continuous monitoring. The results show that the 1.742 μm absorption spectrum can be used to measure HCl concentration. The analyzer has the advantages of short response time, high reliability and the measurement does not be interfered by background gas, dust and window stains.