Tight sandstone gas reservoirs have low porosity and permeability, and their micro pore throat size is small, making them prone to water lock damage during production and fracturing processes. In order to conduct research on the mechanism of waterproof locking in tight reservoirs, the conventional core self suction experiments, waterproof locking agent inhibition of water locking damage experiments were combined with low-field nuclear magnetic resonance technology to reveal the waterproof locking mechanism in micro and nano pore throats of tight sandstone reservoirs from a microscopic perspective, providing a theoretical basis for research on waterproof locking in dense sandstone gas reservoirs. The research results show that after adding waterproof lock additives, the surface tension of the fluid decreases, the contact angle increases, the self suction rate slows down, and the permeability recovers to a certain extent. On this basis, the liquid phase water lock retention phenomenon of the slowly self absorbing phase liquid at different pore throat scales was evaluated from a microscopic perspective through nuclear magnetic resonance T₂ spectroscopy. After adding waterproof lock additives, the average proportion of the self absorbing liquid phase at the smaller pore throat after 20 h of self absorption is 38.61%, and the overall average proportion of the liquid phase at the pore throat is 35.79%. In the sample without the addition of waterproof lock reagent, the liquid phase proportion at the smaller pore throat is 67.48%, and the overall pore throat proportion is 54.52% after 20 h of self absorption. Through the experiment of inhibiting water lock damage with waterproof locking agent, the recovery degree of permeability after adding waterproof locking agent ranged from 15.38% to 20.19%, and the average decrease in the proportion of overall liquid phase retention is 10.73%. The waterproof locking agents effectively reduce the proportion of liquid phase retention in smaller pores, reduce fluid surface tension, and increase core hydrophobicity. This reveals the mechanism of waterproof locking in tight sandstone gas reservoirs, providing theoretical support for reducing water lock damage and improving flowback efficiency in tight sandstone gas reservoirs, and achieving efficient development.