Abstract: In order to probe into the transfer process of grouting pressure in an annular tail void during the backfill grouting of a shield tunnel, rheological properties of cemented mortar were tested by rotary viscometer. The experimental result indicates that the cemented mortar is a Bingham fluid, and its plastic viscosity and shear stress vary respectively from 1 to 4 Pa·s and from 10 to 40 Pa. The Bingham fluid was used to describe the rheological properties of the cemented mortar, and expressions for grouting pressure in the annular tail void were derived. The validity of the expressions was certified by the monitoring results obtained from the Sophia rail tunnel.