[Objective] This study aims to propose a new grouting technology to effectively solve the anti-seepage problem of fully-strongly weathered granite strata by optimizing grouting technology and material mix proportion, and to investigate the anti-seepage effects of frequency-pressure grouting technology in such strata. [Methods] An anti-seepage project of fully-strongly weathered granite strata in the upper reservoir of a pumped-storage power station under construction was taken as the research object. An equilateral triangle hole layout was adopted, and five groups of grouting tests (A, B, C, D, E) were conducted sequentially in Ⅰ, Ⅱ, and Ⅲ holes. The influences of grouting technologies (constant-pressure grouting and frequency-pressure grouting), grouting hole spacing (60, 120, 180 cm), and grouting materials (pure cement slurry and cement-bentonite mixed slurry with five water-to-cement ratios of 5∶1, 3∶1, 2∶1, 1∶1, and 0.5∶1) on the anti-seepage effects of grouting in such strata were compared and analyzed. The grouting effects were further evaluated using permeability tests, single-hole ultrasonic tests, single-hole shear wave velocity tests, and borehole color television tests. [Results] Field grouting trials demonstrated that frequency-pressure grouting technology significantly optimized the grouting effect of fully-strongly weathered granite strata through dynamic pressure adaptation and precise flow control, and it was superior to traditional constant-pressure grouting in terms of permeability coefficient control, material cost efficiency, and fracture filling integrity. Cement-bentonite mixed slurry had better controllability than pure cement slurry, especially in addressing leakage during grouting, and it also greatly reduced the large grout consumption caused by grout leakage and the extended construction period caused by multiple waiting times for grout to set. For fully-strongly weathered granite strata with low strength and loose soil, water pressure tests could not be completed, and only water injection tests were conducted to assess permeability before and after grouting. Single-hole shear wave velocity tests could reflect the density of strata before and after grouting to some extent. Grouting spacing in the range of 60-180 cm had no significant effect on the grouting outcomes, whereas the use of frequency-pressure grouting technology effectively improved the compactness of strata and notably increased shear wave velocity. After frequency-pressure grouting treatment, the permeability coefficient of fully-strongly weathered granite strata decreased from the order of magnitude of 10^-3 to 10^-5, indicating a great improvement in anti-seepage capacity. This demonstrated the feasibility of applying frequency-pressure grouting technology for anti-seepage treatment of fully-strongly weathered granite strata, and it could partially or completely replace the traditional cut-off wall scheme, thereby simplifying anti-seepage treatment, reducing construction cost, and minimizing strata excavation. [Conclusion] Compared with traditional grouting methods, frequency-pressure grouting can smoothly adjust grouting pressure and inflow rate according to the characteristics of the grouted strata and real-time grouting feedback, which can avoid excessive fracturing of low-strength strata, uncontrolled grout diffusion, and excessive grout consumption. This technology can be applied to anti-seepage treatment of fully-strongly weathered granite strata. Combined with cement-bentonite mixed slurry, this technology can effectively solve problems such as grout leakage and excessive grout consumption encountered with traditional grouting methods.