After commercially pure titanium (CP-Ti) annealed sheet was cold-rolled to 9% reduction, electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) were employed to evaluate activated slip and twin in the samples. Meanwhile, the activation of slip systems in deformed grains and the interaction between grains were simulated by reaction stress (RS) model, in which the plastic deformation process in a grain was regarded as a combined consequence of external stress and statistically varied intergranular reaction stress. The results indicate that the reaction stress model is suitable to estimate the deformation behavior of polycrystalline titanium. The model predicts slip occurring in deformed titanium grains, which is confirmed by experimental data. The distribution of slip and twin in deformed grains is non-uniform, connecting to uneven in-grain strain distribution. This uneven in-grain strain can also be generated by deformation of adjacent grains with different crystal orientations. When the plastic deformation in a grain shows significant difference from that of its neighboring grain, additional local slips are triggered to decrease the strain inconsistency. The plastic strain is realized by mechanical twinning in some cases, which combines with the active slips to satisfy in-grain and intergranular strain consistency.