Abstract: Cement grouting is used to improve the integrity and to reduce the permeability of rock mass. The design of grouting parameters depends mainly on the engineer's experience and engineering analogy, and the grouting time is generally not included in the design parameters. Based on the diffusing equation for cement grouting in a smooth and straight fracture, the relationship between that of penetration length and the ratio of grouting time is derived considering the Bingham rheological properties of cement grouting and the properties of cement particles. The grouting criterion based on the grouting time is proposed and analyzed in the grouting design and construction considering the distribution of rock fracture aperture. It may provide a reference for the grouting design and construction in similar projects.