The curing process of polyurethanes was investigated with FTIR method. The curves of conversion (α)VS curing reaction time (t) at different temperatures were obtained .The curing reaction of the system was found to be second order reaction. The reaction rate constants and activation energy had been measured. Effect of the use lever of curing agent and temperatures on curing reaction was discussed. The results showed that when the mole ratio of NCO/OH is smaller than 1, the crosslinking reaction take place at high temperature.