Abstract: The purpose of this paper is to make an epidemiological analysis of the mixed distribution of tertian malaria with long and short incubation by mathematical model. Using the Gram-Charlier series and the Marquardt's nonlinear least square dissecting method and the systematic computerized program for the dissection of mixed samples of tertian malaria with different incubation periods over the past 7 years in Changde City, Hunan Province, and discussing the influence of the climatic factor and epidemic process, it has been inferred that there were two kinds of incubation period of tertian malaria in this city. The long incubation period cases and the short ones have formed seasonal excessive distributions during the late spring and during the summer and autumn, respectively. The parameters estimated from the model had an optimal goodness of fitting to practical distribution (P=0.9967). According to the tests for initial data the model was demonstrated to to effective as there was no statistically significant difference between the theoretical and the actual values.