The effect of temperature, pressure and flow on relaxation time, nucleation density, crystallites growth rate, the interrelation among these quantities and the distributions of deformation rate and cooling time during the process determine the morphology distribution in the final injection molded object. A simple model linking all these quantities was developed to describe morphology evolution during the process. The effect of flow on nucleation density and growth rate was described on the basis of a molecular stretch parameter; the molecular stretch evolution being described by a simple nonlinear Maxwell model whose relaxation time, in its turn, is determined by the molecular stretch and, obviously, by temperature, pressure and crystallinity. The transition between spherulitic and fibrillar morphology was related to the local viscous work, which in its turn is related to the evolution of rheology during crystallization. The predictions of the model are compared with the morphology distributions of samples obtained by injection molding with fast mold temperature evolution during the process of a very accurately studied iPP as far as rheology, quiescent crystallization, effect of flow on nucleation and spherulitic growth rates and spherulitic/fibrillar transition. The model predictions reproduce main characteristics of the experimental results for both pressure and temperature evolution and final morphologies distributions.