Clayey-silty hydrate reservoirs in the South China Sea (SCS) are characterized by low permeability, poor strength, and weak cementation. In order to improve the injection effect of reservoir stimulation by high-viscosity grout, this paper proposes a pulsed pneumatic pre-fracturing grouting technology to enhance the injectability of grout and improve overall conductivity of hydrate-bearing sediments. In the pulsed pneumatic fracturing experiment, increasing the frequency ƒ results in higher average pneumatic pressure σavg and maximum pneumatic pressure σmax, maintaining elevated pneumatic pressure levels that reduce local soil strength and improve fracturing effectiveness. In addition, the fracture extension range is positively correlated with the pressure and frequency. In a pulsed pneumatic pre-fracturing grouting experiment, this technology outperformed the conventional fracturing grouting. At frequencies of 2.5 Hz, 5 Hz, and 10 Hz, the total extension distance of the grout consolidation body increases by 3.28, 4.43, and 4.71, respectively. Meanwhile, the total weight of the grout consolidation body increased by factors of 1.94, 2.45, and 3.57. Additionally, under high-frequency fracture initiation condition (10 Hz), the average thickness of the grout consolidation body doubled compared to that under low-frequency condition (2.5 Hz). In conclusion, the pulsed pneumatic pre-fracturing grouting technology significantly improved the injectability of high-viscosity grout and the effectiveness of grouting stimulation in sandy and clayey-silty hydrate-bearing sediments.