The electro-hydrostatic actuator (EHA) is a new type of power-by-wire (PBW) actuation system, which is utilized to realize a more electric aircraft. However, EHA suffers from serious thermal problems, due to its high integration and high power density. Therefore, a reasonable heat dissipation structure is an essential method for solving this problem. In this paper, a novel ribbed honeycomb heat sink (RHCS) developed by combining a ribbed heat sink (RHS) with a honeycomb heat sink (HCS) is proposed. Moreover, the optimization of heat sink parameters was achieved by using a multi-objective particle swarm optimization algorithm (MOPSO). Initially, the thermal resistance and mass models of the HCS were constructed, based on which the optimal structural parameters of the honeycomb cell were obtained. In addition, the thermal resistance model of RHCS was constructed using the response surface method, and parameters such as rib spacing, height and width were obtained based on MOPSO. Finally, the heat dissipation capability of RHCS was verified using both a simulation and experimental methods, and the results show that the heat dissipation capability of RHCS is about 15%∼20% higher than that of RHS and 7.4%∼10.3% higher than that of HCS. The configuration and design method of RHCS proposed in this paper provide a solution for the thermal design of EHA.