Ti6Al4V alloy is the most widely used titanium alloy in orthopaedics. Selective laser melting of porous Ti6Al4V alloy can reduce its elastic modulus, reduce the stress shielding phenomenon, and promote the growth of bone tissue, but the plasticity of the formed parts is usually low. Therefore, rhombohedral dodecahedron porous structures with unit size of 1~2 mm, aperture of 500~1200 μm and porosity of 60%~90% are designed, and the compression specimens are formed by selective laser melting technology. The mechanical properties are studied by compression simulation and experiments, and the effects of annealing heat treatment on their mechanical properties and microstructure are also studied. The simulation results show that more accurate results can be obtained by error compensation for the strut diameter of the model. The experimental results show that when the unit size is 1.5 mm, the compressive strength and elastic modulus of specimens are between 78.16~242.94 MPa and 1.74~4.17 GPa, which are similar to the mechanical properties of human cortical bone. After annealing at 820 ℃ for 2 hours, the compressive strength and elastic modulus of the specimens are basically the same as those of the formed specimens, while the plasticity is improved, so they are more suitable for orthopedic implants.