Abstract: Aiming at the existing problems of underground seam gas pressure measurement sealing hole by cement mortar under complex geological conditions, the paper proposes variable diameter pressuring secondary sealing hole method, analyzes the reliability of the sealing process. Based on finite element theory, the rock roadway model of experimental site is established. Through analyzing stress distribution of rock tunnel, it is achieved that the plastic deformation zone is in the range of 9.5 m from laneway’s side, which provides data support for variable diameter position of first stage borehole. Field application results shows that the variable diameter pressuring secondary sealing hole method by cement mortar can effectively seal the surrounding rock fracture, which can provide support for accurately obtaining the original coal-seam gas pressure.