In order to solve the problem that the traditional detection methods are limited to be unable to achieve accurate positioning function in the specific situation of narrow space, combined with the characteristics of ethylene glycol coolant volatilization and ionization by ultraviolet lamps，a sensor based on photoionization is fabricated, an array sensing method is proposed, by creating a closed space in the prone part of leakage, and placing multiple array sensors in the closed space for detection, the array detection platform for coolant leakage was constructed by combining the data processing module and PC. The test results show that the system has broken through the key technology of real-time online monitoring of coolant leakage in narrow space, and the whole system is sensitive to small leakage. In the simulated micro-leakage test with 0.1ml ethylene glycol coolant, the alarm time is kept within 10s after the alarm concentration is set to 3ppm, and the response is timely and the system is strong scalability, which provides a practical detection method for timely troubleshooting coolant faults in complex cooling environment.