The variation of synchronous grouting pressure has a significant effect on the internal force distribution of adjacent segments. To control grouting pressure accurately and keep safety during shield driving, the grout pressure distributions in space-time domain were investigated. By considering of time-variation behavior of grout viscosity and permeability, the process of grout filling, diffusion and dissipation during shield backfilled grouting were united. Then, the theoretical formulas of grouting pressure distribution along the circular and longitudinal direction of segments were built. Finally, a grout rheological test and numerical models were conducted based on the engineering case, and the time-space distribution law of grout pressure acting on tunnel segments were obtained and analyzed. The results show that the grout consolidation and pressure dissipation during synchronous grouting have notable influence on distribution of grouting pressure along segments. The increase of grout viscosity and decrease of grout liquidity and permeability of soil layers affect the extent of grouting pressure dissipation, and then affect the distribution of internal force of tunnel segments. The mechanical features of segments calculated from numerical models are closer to field measured data when considering the time-varying effect of grout viscosity. The research results provide a guideline for fine analysis of segment mechanics during construction.