Abstract: To investigate the principles governing the evolution of strain energy density and related damage constitutive models during uniaxial rock creep, this study uses uniaxial creep-unloading experiments to systematically examine the creep strain energy density evolution in four types of rocks: 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. Results indicate that (1) the elastic strain energy densities of the four types of rocks show a linear reduction trend with extended creep time, displaying linear decay properties. (2) By combining the results of uniaxial creep-unloading testing, this study proposes a method for calculating rock creep strain energy based on the linear decay properties of elastic strain energy density. (3) 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. (4) As creep time advances, the ratio of dissipative strain energy to input strain energy density in rocks increases, peaking 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. (5) A viscoelastic-plastic-damage coupled constitutive model has been developed based on the dissipation mechanism of strain energy, effectively representing the behavior of rocks with varying brittleness along the creep curve.