Abstract: Hardness of materials is a mechanical property widely used in material science and engineering. Based on energy equivalent principle, a semi-analytical prediction model is proposed to obtain Brinell hardness and Rockwell hardness if materials are uniform, continuous, isotropic and their stress-strain relations conform to Hollomon-law. The hardness can be determined by Hollomon-law parameters of materials. Several parameters in the prediction model are determined through finite element analysis (FEA). For a wide range of assumed materials, a large number of FEA calculations are carried out to verify the prediction model. The results show that the model generates a good prediction. For six kinds of tested ductile metallic materials by hardness test, the Brinell hardness and Rockwell hardness predicted by the model are in good agreement with the hardness test results.