In order to avoid the risk of water inrush and mud gushing during highpressure waterrich karst tunnel construction, improve the working condition and shorten the construction schedule, the problems of orginal fullface advance grouting scheme in construction of a highpressure waterrich karst tunnel in China are analyzed. And then the original construction scheme is optimized in terms of opening design, grouting materials and grouting parameters. Finally, a fine advance grouting technology, sealing outside and reinforcing inside applied to upper crosssection, is proposed. The application results show that: (1) Drilling holes in upper crosssection of tunnel face can avoid repeated work of drilling platform disassembling and assembling, which can reduce construction period by 4 days per cycle. (2) According to the principle of one hole for multipurpose and grouting while examining, the grouting effect of previous holes can be examined, which can achieve rapid excavation. (3) By using sulphoaluminate single slurry, the water stop effect and rapid excavation can be guaranteed. The site application shows that the grouting time per cycle is increased by 61.11% and the grouting material per cycle is reduced by 47.79%.