FT-IR,NMRand high-resolution MS were used to characterize the chemical structure of toluene diiso- cyanate (TDI)-trimethylolpropane (TMP) prepolymer,and HPLC-MS was adopted to detect the concentration of each oligomer in the reaction intermediates and to further reveal the reaction kinetics of TDI and TMP.The results indicate that (1) the TDI-TMP addition reaction is a second-order reaction; (2) temperature significantly affects the reaction selectivity of 2'-and 4'-NCO in TDI; (3) the 2'-NCO selectivity increases from 0. 41 to 0. 64 when the temperature increases from 50℃ to 80℃; (4) the reaction rate constants of the three steps of the reaction at 80℃ are 0. 18540,0. 03789 and 0. 01140mol^-1 ·L^-1 ·min^-1 ,respectively,with the corresponding activation energy be- ing 12. 76,16. 58 and 25. 63 kJ/mol,respectively; and (5) the third step of the reaction is more sensitive to temperature than the first two steps,so that appropriately raising temperature in the later reaction may result in a more sufficient reaction.