An experimental system for detecting multi-component toxic gases,which is based on the near-infrared wavelength modulation spectroscopy and harmonic detection technology,is established by taking use of time division multiplexing method. Detecting multi-component toxic gases (CO2,CO,HCN) generated by a fire at one time is completed by this experiment. The full-scales of the three gases are 400×10-6,400×10-6 and 300×10-6. The data carried from the detector is processed simultaneously while the gases are being monitored. The results show that the error between the real gas concentration and the measured gas concentration is less than 0.73% of the full scale. Therefore,this system has a fine linearity and can reach sensitive level for gas detection.