Capacity enhancements are sometimes observed when carbon materials, especially porous carbons, are used as lithium-ion batteries anodes. However, the correlative mechanism is unclear now. Here, porous carbon (PC) is used to reveal the mechanism by using a combination of structure analysis and electrochemical calculations. The coexistence of blind pores and closed pores with fractal porous structure is confirmed by N-2 sorption and small angle X-ray scattering. When the PC with main pore diameter of 30 nm is used as lithium-ion batteries anode, the specific capacity increases from 700 mAh g(-1) (40th cycle) to 1300 mAh g(-1) (110th cycle) at a current density of 50 mA g(-1). It could be ascribed to the stepwise diffusion of Li atoms inside the pore structure, including the following two effects. (1) The diffusion of solvated Li+ in the blind pores results in the continuous formation of solid electrolyte interface, providing more activated sites on the inside surface; (2) Li atoms diffuse into the inner closed pores via disordered carbon walls to further enhance the reversible capacity. Our finding provides a deep insight on the mechanism of capacity enhancement of porous carbon electrodes, which could benefit the design of advanced electrode materials. (C) 2017 The Electrochemical Society. All rights reserved.