With the advancement of power systems, large oil-immersed transformers play a critical role in ensuring grid stability. However, transformer fires caused by internal faults pose significant risks, including explosions and widespread power outages. This study proposes an automatic water spray fire extinguishing system to address these challenges. The system integrates real-time fire detection, automated water spray activation, and a dual-pump redundancy mechanism. Key components include temperature/smoke sensors, an AT89C52 microcontroller, and a water spray network. The system’s design emphasizes rapid response, cooling effects, and oxygen isolation through fine water mist. Experimental validation confirms its effectiveness in suppressing fires within 60 seconds, reducing potential losses by 90% compared to manual interventions. This solution enhances the safety and reliability of high-voltage transformers, offering practical value for power infrastructure protection.