Surface doping is a common method to improve the performance of nanostructured materials. Different dopants will affect the structure and catalytic reactivity of the support. For a comprehensive understanding of the doping effects of metals doped into CeO2, we conducted density functional theory (DFT) studies on the stabilities and geometry structures of transition-metal atoms (M = Fe, Co, Ni, Cu; Ru, Rh, Pd, Ag; Os, Ir, Pt, Au) doped into CeO2 (111), (110), and (100) surfaces. Moreover, the reactivity for H-2 dissociation and oxygen vacancy formation are systematically investigated on M-doped CeO2 (100) surfaces. The greater the binding energies of doped M atoms on the CeO2 surface, the more difficult the formation of oxygen vacancies. The doped Co and Ir atoms do not directly participate in H-2 activation but serve as a promoter to make the H-H bond to break easily. The Cu, Ru, Pd, Ag, Pt, and Au atoms could act as the catalytically active center for H-2 dissociation and greatly reduce the activation energy barrier. Besides, it is easier to generate H2O (W-M) and a surface oxygen vacancy from the intermediate H2(M)/H4(M) than from H3(M)/H5(M), which is related to the acid-base interaction between H-Ce/M* and HO* in H2(M)/H4(M). This work could provide theoretical insights into the atomic structure characteristics of the transition-metal-doped CeO2(100) surface and give ideas for the design of hydrogenation catalysts.