To enhance boiling heat transfer for promoting the efficiency of the energy system, the porous surfaces with structural gradients were developed on pure copper substrates by employing the electrochemical deposition method. In this study, honeycomb-like porous structures and hierarchical axial honeycomb gradient porous structures were fabricated using constant current single-step deposition and constant current constant voltage two-step deposition methods, respectively. Saturated pool boiling heat transfer experiments were conducted using HFE-7100 as the working fluid to investigate the influence of the gradient pore size changes on the boiling heat transfer performance of porous surfaces. The results demonstrated that the hierarchical gradient porous surface, which had a total deposition time of 60 seconds and an increased second-step deposition voltage of 3 V, showed the most significant heat transfer enhancement. The wall superheat at the boiling initiation point was 9.5 K, a 43.00% decrease compared to the smooth surface at 16.8 K. Moreover, the critical heat flux and heat transfer coefficient reached 522.02 kW/m2 and 22.76 kW/(m2?K), respectively, exhibiting with enhancements of 193.40% and 261.01% compared to the smooth surface. The hierarchical porous surface had two types of nucleation sites: internal pores and dendritic protrusions. The micropores and the internal micropores of the dendrites exhibited a wide range of pore sizes. This extensive distribution of pore sizes not only increased the density of nucleation sites and effective heat transfer area but also reduced the nucleation energy barrier. The axial pore size gradient accelerated bubble evolution, and the capillary suction force provided by the gradient porous structure and dendrites facilitated the return flow of the working fluid to the nucleation sites both horizontally and vertically, thereby enhancing the boiling heat transfer coefficient and critical heat flux of the hierarchical gradient porous surface.