The work aims to study the effect of the relative density and pore size of open-cell aluminum foam with spherical pores on the mechanical properties of aluminum foam-polyurethane composites and their energy absorption properties. The prepared aluminum foam-polyurethane composites were subject to quasi-static compression experiments. Through the quasi-static compression experiments, the corresponding stress-strain curves were obtained and the energy absorption-strain curves were deduced from the stress-strain curves. When the pore size of aluminum foam was constant, the relative density of aluminum foam was increased from 35.0% to 38.4%, and the yield strength of aluminum foam-polyurethane composites was increased by 6.5 MPa. When the relative density of aluminum foam was constant, and the pore size of aluminum foam was increased from 5.5 mm to 9.5 mm, the yield strength of aluminum foam-polyurethane composites was increased by 3.38 MPa. The relative density and pore size of aluminum foam have a great influence on the properties of aluminum foam-polyurethane composites. The larger the relative density of aluminum foam is, the better the composite properties are. The larger the pore size of aluminum foam is, the better the composite properties are; moreover, the larger the relative density of foam aluminum is, the better the energy absorption property of the composites is; the larger the pore size of aluminum foam is, the better the energy absorption property of the composites is.