Abstract: Along with the prolonging of people-s staying time in enclosed environments such as spacecraft, aircraft, submarine and so on, air pollution in the cabin has become a main factor which endangers missionaries- life safety. To improve the ability of these enclosed environments in dealing with sudden contaminant, a novel discrete concentration stochastic model was established. The sensitivity analysis algorithm which can identify source location and strength was presented. Then the dynamic identification of source emitting characters and prediction of contaminant concentration were realized using combined implicit and explicit Kalman filter. The identifiable zone of different sensor placements was analyzed, and the best scheme of sensor placement had been found. Simulation results prove that the sensitivity analysis algorithm and combined implicit and explicit Kalman filter can realize the dynamic identification of source emitting characters and prediction of contaminant concentration speedily and accurately.