By means of regression analysis, an insight into the limitations of the widely used Freeman and Carroll, method is offered and it is indicated that the Freeman and Carroll method is essentially unstable for the determination of the reaction order. The reliabilities of the intercept and slope terms for any one regression equation are also investigated mathematically, suggesting that the slope term is in general easily to be determined accurately, whereas the intercept term has possibility to be obtained with great error. Based on these theoretical analyses, a new method to calculate the kinetic parameters for polymer thermal degradation is proposed, in which the three kinetic parameters are determined from the slopes of three regression equations described in this paper. The experimental data in the literature are used to verify the proposed method. By comparing the results from the Freeman and Carroll method and the proposed method respectively with those from the Doyle method, it is shown that the proposed method can be applied with a much better accuracy than the Freeman and Carroll method.