In a burst of toxic and hazardous substance spills, the quick acquisition of the leak source information is one of the difficult issues in the analysis of production safety and accident predictions. The inverse problem of the heavy gas leak source is an important step to establish a reliable heavy gas leakage diffusion model, for the heavy gas spill control and the heavy gas leakage management. The paper discusses the source term inversion after the chlorine gas pipeline leakage and diffusion in the obstacle environment. Combining the MCMC sampling method based on the Bayes inference theory with a Chloroacetic acid production factory production plant layout and a chlorine gas diffusion prediction model, the key parameters of the leak source such as the location and the intensity, are obtained by the inverse method, and it is shown that the results of these parameters are within the range of the true values.