Abstract: To investigate the principles governing the evolution of strain energy density and develop related damage constitutive models during uniaxial rock creep, uniaxial creep-unloading experiments was performed to systematically examine the creep strain energy density evolution of coal, mudstone, white sandstone and red sandstone. The focus is on exploring the conversion and dissipation mechanisms of strain energy density during rock creep and developing damage creep constitutive models for rocks of varying brittleness. The results show that the elastic strain energy densities of the four types of rocks show a linear reduction trend with extended creep time, displaying linear decay properties. Further, a method for calculating rock creep strain energy was proposed based on the linear decay properties of elastic strain energy density. The dissipative strain energy density, along with the input strain energy density for rocks categorized by four grades of brittleness, increases over time and can be divided into stages of decay growth, uniform growth, and accelerated growth. As creep time advances, the ratio of dissipative strain energy to input strain energy density in rocks increases, reaching the peak at the critical post-peak point during accelerated creep, where more brittle rocks show a larger proportion of dissipative strain energy density relative to input strain energy density. A viscoelastic-plastic-damage coupled constitutive model has been developed based on the dissipation mechanism of strain energy, effectively describing the behavior of rocks with varying brittleness along the creep curve.