The invention discloses a method and device for on-line monitoring of precision processing powder resin leakage. The device includes a sampling system and a detection system, the sampling system includes a sampling globe valve, a sampling pressure-reducing valve, a sample injection globe valve, a sample injection pressure-maintaining valve, a testing pipeline blowdown valve and the like, and the detection system includes a transparent plexiglass filter box with a filter membrane, a filter box water inlet pressure gauge, a filter box water outlet pressure gauge, a differential pressure gauge, and an audible and visual alarm. According to the method, the transparent plexiglass filter box with the filter membrane is a core component of the device, on the one hand, a pressure difference is formed, an alarm is given, and the on-line monitoring function is achieved; on the other hand, the transparent and visible filter membrane is arranged to facilitate daily regular inspection, and when thedevice sends out a leakage alarm, personnel goes to the site to visually observe the situation of powder resin collected on the filter membrane to verify whether the alarm prompt is accurate or not,so as to realize final manual confirmation; and the pressure difference between the filter box water inlet pressure gauge and the filter box water outlet pressure gauge is calculated through the differential pressure gauge, and the audible and visual alarm sends out a sound and light alarm after receiving a signal.