A plurality of monitoring devices are arranged at different heights and steps, and infrared reflective assemblies of the monitoring device are set at different heights to collect infrared spectral data of chemical constituents of the air mass that are being diffused in airspace of different heights. The pollution factors contained in the air mass and the pollution level of each factor are learned by using IR spectrum for qualitative and quantitative analysis on the pollution factor, therefore realizing continuous monitoring in a certain area. Artificial duty is not required while 24-hour continuous intelligent monitoring can be achieved. Besides, meteorological data are collected in combination with the meteorological data collected by the meteorological information acquisition module at different heights and calculation is made based on the air diffusion model of various pollution factors to finally determine the position of air pollution source.