In order to accurately calculate the flow number(FN) of asphalt mixture under repeated load permanent deformation test, shortcomings of the existing calculation methods are analyzed, and a local strain rate method is proposed. Firstly, based on Francken model and FNest model, the differences between strain method and strain rate method are studied; Secondly, the change trends of the flow number with K values of Francken strain rate model and Hoerl strain rate model are studied, and the optimal K value of this experiment is determined; Finally, the superiority of local strain rate method is studied. The results show that, high goodness of fit of strain model can not guarantee that the derivative of the corresponding strain fitting curve has a high goodness of fit, and goodness of fit of strain rate curve obtained by strain rate method is higher than strain method; With the decrease of K, the FN of Francken strain rate model decreases gradually, while the FN of Hoerl strain rate model increases gradually, and relative error of FN between the two models decreases gradually. The optimal K value of this experiment is 1.5; Compared with local strain rate method (K=1.5), Francken global strain rate method overestimates 14.4%, Francken global strain rate method overestimates 10.8%, Hoerl global strain rate method underestimates 11.0%, FNest global strain rate method overestimates 27.8%, FNest global strain rate method overestimates 49.2%; Relative error between the two models of local strain rate method (K=1.5) is significantly lower than that of global strain rate method.