Abstract: Accurate determination of coal seam gas pressure is the effective protection of the prediction and prevention of mine gas,drilling water gushing and hydrocele problem are often encountered in measuring downward cross-layer borehole pressure process in rich water surrounding rock,which not only increase the difficulty of grouting sealing,but also influence the authenticity and reliability of the original gas pressure because of the impact of water pressure.To solve above problems,this paper attempts to explore the drainage and sealing method under the conditions of water gushing and hydrocele in downward cross-layer gas pressure determination borehole.The field practice in Gedian mine of Shenhuo coal and electricity group proved that this method can effectively avoid the adverse effects of residual water and continued gushing caused by downward cross-layer gas pressure determination borehole and can more accurately measure the original gas pressure of the coal seams.