<p>Apparent viscosity is a key parameter in the rheological constitutive relationship of fresh cement paste and can also serve as a structural parameter characterizing its thixotropy behaviour. This paper establishes an apparent viscosity model for cement paste based on the thixotropic equation of a non-Newtonian fluid, using the volume fraction of solids as a bridge between hydration and thixotropy. The model accounts for both the breakdown phenomenon and the irreversible increase in apparent viscosity at early stage. The apparent viscosity of cement pastes with various water-to-cement (w/c) ratios under various strain rates can be obtained, reflecting their thixotropic evolution. Model validation through experimental comparisons confirms its accuracy. The results demonstrate that the model can effectively predict and control the thixotropy of cement paste.</p>