<p>This paper aims to establish a novel mechanical damage constitutive model (MDCM) of geomaterials under uniaxial compression, which is of great significant to the theoretical research of geotechnical engineering. Firstly, an exponential function of strain difference was constructed to better simulate the initial compacted stage of geomaterials than existing models. Secondly, based on the equivalent strain principle, Weibull random distribution and the strain difference function, the novel MDCM considering the whole deformation process of geomaterials was established, whose parameters were solved using linear regression method and continuous boundary conditions. Then, the rationality of the proposed MDCM was verified using stress–strain curves of dense and cracked geomaterials in uniaxial compression tests, offering better fittings than existing models. In addition, the superiority and the general applicability of the proposed MDCM was evaluated, especially in simulating the post-peak deformation curves of geomaterials, and an experimental verification was carried out utilizing the uniaxial compression results of red sandstone. Finally, the applications and limitations of the proposed MDCM were discussed carefully. The results greatly enrich the theoretical research of MDCM of geomaterials.</p>