To improve the heat transfer performance of Hydraulic Exoskeleton Robot’s oil tank, three dimensional (3D) numerical simulation, based on Computational Fluid Dynamics (CFD), is performed on finned oil tank with different fin structures. The performance characteristics curve of the average heat transfer coefficient (h), the pressure drop(Δp) and the comprehensive evaluation coefficient JF factor (JF), varied with the fin structure under the different wind velocities, were obtained. The research results show that h decreases but Δp increases with the increase of fin thickness at the range of 0.5～0.9 mm;h increases but Δp decreases with the increase of fin spacing at the range of 2.1～2.9 mm; the h and Δp increase with the increase of fin height at the range of 10.5～14.5 mm. Finally, when the fin thickness is 0.5 mm, the fin spacing is 29 mm and the fin height is 12.5 mm, the heat transfer performance of the fin unit is optimal. The simulation results provide a reference for the optimization design of the finned oil tank structure.