The water in grout will permeate toward surrounding rock due to the osmotic pressure, so that the grout itself will consolidate gradually during shield backfilled grouting; and the grouting pressure will dissipates slowly. The variation of grout viscosity will lead to a change in the permeability of soil layers during the grouting process. Based on this fact, the grout consolidation and pressure dissipation equations have been deduced; and the distribution regularities of grouting pressure acting on segments have been analyzed, which provide a guideline for fine analysis of segment mechanics during construction. The results show that: the increase of grout viscosity will result in decreases in the grout liquidity, the extent of grouting pressure dissipation and duration time of grout dissipation. The variation of grout mixing proportion and permeability coefficient of surrounding rock can also influence the extent of grouting pressure dissipation and duration time of grout dissipation.. The calculated results are consistent with the field measured results. It is suggested that the grout dissipation effect due to time-varying should be taken into account in backfilled grouting.