Ultra-high pressure grouting of hydropower project building is a new subject. The natural fall of the second pumped storage power station of Tianhuangping is about 730m, 12MPa grouting experiment was carried out in PDX1 testing tunnel of Tianhuangping to study and explore the impact of high water head in hydraulic tunnel on the integrity of tunnel surrounding rocks and deformation resistance. By the smooth progress of the entire filling based on the appropriate construction methods and measures, reasonable grouting procedures and parameters were obtained, which could be the practical basis of large concrete lining grouting with high pressure water head.