Abstract: As an inorganic cementitious material with low cost and good property, cement grouts has been widely used in many engineering fields such as highways, tunnel, slopes, foundations, railways, construction, mining and water conservancy. As for cement grouts, the rheological properties of cement grouts are significantly affected by the changes of the hydration time and the water cement ratio, which determine the diffusion state of cement grouts in rocks and soils and have a great influence on the outcome of projects. However, the current research only considered the influence of a single factor on rheological properties of cement grouts, the combined effect of these factors has not been well understood. In this study, Portland cement grouts, a widely used material in practical grouting engineering are used as the research object and the Portland cement grouts with four water cement ratios which are the typical cement ratio of Newtonian fluid (1.5, 2.0, 5.0,10.0) at six moments (0,5,10, 20, 30 and 60 min) were chosen as the experimental group, then combined with the numerical analysis and the theoretical method the effect of hydration time and water cement ratio on rheological properties of Newtonian cement grouts was studied. The results show that: the hydration time and the water cement ratio both have significant influence on dynamic viscosity of Newtonian cement. The former shows a trend of growth, and the longer the hydration time is, the faster the growth trend, the latter shows a trend of decreased, and the smaller the water cement ratio is, the more significant the decreasing trend. Combined with the perspective of statistical theory, practical applicability and accuracy, this study selects four theoretical models to discuss the quantitative relationship of the effect of hydration time and water cement ratio on rheological properties of Newtonian cement grouts, and the four theoretical models are the most basic in mathematics, also the most widely used in practice: the linear model, exponential model, power function model and logarithm model. Then the optimal model will be determined from the fourth according to statistical theory and experimental verification. Comparing the determination coefficients and the regression values of the four fitting models, the exponential model is the optimal model for the quantitative change of dynamic viscosity of Newtonian cement to react the effect of hydration time and water cement ratio on rheological properties of Newtonian cement grouts. The difference between the theoretical value and the experimental value of the exponential model is within 10%, while more than 80% of the difference between the theoretical value and the experimental value of linear, logarithmic and power function models are greater than 10%. Thus, the rheological equation of Newtonian cement considering the hydration time and the water cement ratio are built. The research results can not only improve the rheological theory of Newtonian cement grouts, but also provide certain technical support for practical engineering applications such as the building foundation support, tunnel water plugging and seepage prevention, foundation reinforcement, geological disaster prevention and control, and agricultural soil conservation.