Abstract: Aim To study the effect of various kinetic factors on the formation of simultaneous interpenetrating network(SIN). Methods The consuming of NCO group of PU and CC group of GMA was monitored through FTIR to obtain the conversion rate vs. time curves. Results and Conclusion The difference between the reaction situations of the respective component in SIN and the pure respective component was investigated. The PU and PGMA reactions in plasticized SIN all follow the second order kinetic mechanism and their activation energies are 28 1 and 35 6 kJ/mol respectively. As the PU catalyst was changed, the different gelation sequences are determined according to the conversion rate curve obtained through FTIR and the relation between conversion rate and gelation point.