Toluene diisocyanate (TDI) is a widely used intermediate in the production of polyurethanes. Phosgenation reaction is the most important operation in the process of producing TDI, which is commonly performed in a jet reactor. Because of the high toxicity of phosgene, it is unpractical to evaluate the performance of the reaction by sampling intermediate products. To overcome this difficulty, first, a mapping table was created for reaction path and temperature. Next, various parameters that affect temperature, such as reaction path, ratio of phosgene, diethyl iso-phthalate (DEIP), etc. were investigated by simulation studies. The results show that the ratio of phosgene is the most important parameter. On the basis of the mapping table, easily available experimental reaction temperature data can be utilized to infer the reaction path, and consequently the performance of jet reactor can be predicted. The method was validated after being used in an experimental setup of 1000 tons/annum TDI capacity.