The hydrogen chloride is harmful to the environment and causes water pollution.It is mostly produced by the incineration of urban living garbage,medical waste and so on. According to the limitations of volumertric method for nitric acid silver,thiocyanate mercury spectrophotometry and ion chromatography to monitor the hydrogen chloride gas, multiple reflecton cell Fourier transform infrared spectrophotomery method is presented to detect the hydrogen chloride gas concentration. Based on accurately measuring the infrared absorption spectrum of the hydrogen chloride gas, spectrum is quantitatively analysised by using nonlinear least square algorithm in order to get the hydrogen chloride gas concentration. With the concentration results under laboratory conditions,this mehod is also effective way to quantitatively analyse the hydrogen chloride gas.