Abstract: The kinetic parameters of main elementary reactions for pyrolysis of paraffins are predicted according lo the dependence of structure -reactivity proposed by the authors. The pyrolysis for a mixture of ethane-propane based on different reaction networks are simulated and compared with pilot data. Thus a reaction network which can describe the process properly and really and has a smaller reaction number is proposed in this paper. Gear method is used to solve the structural kinetic model of C4 paraffin pyrolysis. The predicted product distributions based on the model agree well with pilot data published in the literature.