The present study provides an extensive parametric evaluation for the effect of water pressure on Mega Tunnel stability in the difficult Himalayan terrain. Subterranean structures like tunnels must be stable for safe and sustainable infrastructure development. It is crucial to comprehend how Mega Tunnels behave under different water pressures in the Himalayan region, where geological and hydrological circumstances present particular difficulties. The study applies parametric analysis and advanced numerical simulations to evaluate water pressure effect on tunnel stability. To assess essential markers of structural integrity, such as deformation and crown displacement, the study focuses on analyzing key factors. A variety of water pressure situations are taken into consideration to portray the dynamic character, reflecting real circumstances in the Himalayas. Employing advanced computational modelling techniques, the methodology includes consideration of hydraulic and geotechnical issues that are specific to the geology of the Himalayas. The parametric study findings offer insightful information about how tunnels react to different water pressures, illuminating possible failure modes and suggesting best practices for design. The research findings provide useful suggestions for tunnel design, construction, and maintenance, thereby advancing the field of tunnel engineering in the Himalayan areas. The results highlight the necessity for adaptive engineering solutions to assure the long-term stability and resilience of underground structures in difficult geological and hydrological contexts, with wider implications for infrastructure development in mountainous terrains worldwide.