To overcome the persistent challenge of unstable water control efficacy observed in field tests for high-temperature, high-salinity gas reservoirs with excessive water production, the performance mechanism of a developed in-situ self-emulsifying nanoparticle-enhanced, oil-selective water control agent was investigated. Using a high-temperature and high-pressure micro-shear emulsification method that simulated reservoir conditions, the interfacial structure and dynamic/static structural stability of the generated Pickering emulsion were examined. The synergistic effect strength differences in forming Pickering emulsions among different water control system compositions were compared. Results indicate that the synergy between nanoparticles and emulsifier can form a highly internal W/O Pickering emulsion with formation water four times its own volume. This emulsion exhibits tolerance to high temperature and high salinity, possessing solid-like structural properties. Furthermore, the highly stable three-dimensional structure formed by nanoparticle aggregation within the continuous oil phase imparts strong dynamic structural stability to the water control system. Rheological curves show that the initial deformation of the Pickering emulsion causes the fracture of the three-dimensional structure in the continuous phase, leading to the directional arrangement of nanoparticles and the formation of a more stable multi-point connection structure. This increases the critical strain at which water control capability remains stable during water phase blockage. The findings provide deeper insights into the in-situ emulsification process and the water control mechanism of Pickering emulsions, establishing a theoretical foundation for their improvement.