The grain orientation and grain shape changes of commercial pure titanium after low rolling deformation were observed using scanning electron microscope and backscattering electron diffraction techniques, and the actual active slip systems during deformation process were analyzed statistically. The mechanical interaction between grains and its influence on the slip systems selection and orientation evolution of grains were studied. The active slip systems and orientations’ evolution of rolling grains were simulated using Sachs model and Reaction Stress model. The results show that the plastic strain of grains in the polycrystalline commercial pure titanium is not in accordance with Taylor deformation principle, and the Sachs model can partly reveal the mechanism of slip and trend of the orientation evolution. The plastic deformation of grains depend not only on the external stress, but also on the reaction stress between grains, which influence the selection of slip systems. The Reaction Stress model based on the grains’ interaction can be used to reveal the activation process of the slip systems more comprehensively, and to predict the grain orientation after deformation more accurately. The reaction stress between grains is influenced by many factors, among which, the orientation of grains and its relation to the grain orientation have important impact on the magnitude of the reaction stress.