An all-optical fiber sensing system based on fluorescent fiber is proposed to detect partial discharge faults during ground simulation experiment for the high-voltage supply system in the cabin of a near-space vehicle. The partial discharge response parameters in the equivalent vacuum state of near space are obtained, and the equivalent ground height of the proposed system is more than 20 km. A partial discharge fault in the vacuum cabin of the flight vehicle with a diameter of 86 cm can be detected. Experimental results confirm that the proposed all-optical sensing system has suitable optical electron response and sensing characteristics for partial discharge faults at different pressures.