The relationships between H, O, P, S, and N impurities and the type of plasticity mechanism displayed in Ni were studied using density functional theory. We found that different impurities have different segregation tendencies with regards to Ni. S, P, O, and H are most likely to occupy sites on the Ni surface, especially when S and P are the impurities. S, P, H and O have little effect on the deformation mechanism of Ni when located in the grains of the Ni metal. Conversely, N prefers to occupy these grains, readily promoting the dissociation of dislocation into segments, and making cleavage fracture less likely to occur, which enhances dislocation nucleation. S, P and N caused a decrease in the plasticity of Ni, but H and O increased the probability of twinning for Ni. However, these impurities do not switch the deformation mechanism of Ni from dislocation-mediated slipping to twinning.