Abstract: The pressure distribution around tunnel and along the axis is important for effective synchronous grouting to support ground strata. Based on the theory of hydromechanics, the filling pattern and mechanism of synchronous grouting are studied. The mechanical model of circumferential and longitudinal filling is analyzed. Formulae for grouting pressure are deduced respectively for Newtonian fluid and Bingham fluid. Parameters in the formulae including synchronous grouting volume, the type of grouting materials and the gap size of the tunnel are also analyzed. The results show that the pressure decreases from the maximum at shield tail along the tunnel axis and is affected significantly by the static shear strength of grouting and the shield tail void size. These conclusions are useful for the renovation of grouting materials and the accurate control of synchronous grouting.