Abstract:The adult periods of some insect groups are longer than that of the larva. This fact often causes the generation overlap and the estimation of the intrinsic rate of increase (rm) become difficult. An improved model was established to estimate the parameters of the fecundity table of experimental population of these insects according to the matrix principle. This improved model enabled the number of offspring‘s propagation be calculated during the survival period of female adult of the former generation. The results showed that rm of the insects whose generations overlap significantly could be calculated successfully through the model. According to the checking computations, the rm value calculated from this improved model was more closely to the exact value than that of calculated from the un-improved model.