The utility model relates to a dielectric loss on-line monitoring device for a capacitive device based on IEC61850-9-2 standards. The dielectric loss on-line monitoring device comprises a voltage mutual inductor, wherein one end of the voltage mutual inductor is connected with a bus or a circuit, and the other end of the voltage mutual inductor is connected into a merging unit which inputs a reference voltage signal to a dielectric loss measurement unit with the IEC61850-9-2 standards through an optical fiber. A clock unit accesses a B code timing signal into the dielectric loss measurement unit through an optical fiber, the dielectric loss measurement unit is connected with a comprehensive monitoring unit or a station end monitoring unit, and a high-accuracy current mutual inductor with zero magnetic flux leakage is sleeved on a grounding line of the capacitive device to enable a voltage signal output by the mutual inductor to be accessed to the dielectric loss measurement unit installed on site. By means of the dielectric loss on-line monitoring device for the capacitive device based on the IEC61850-9-2 standards, the dielectric loss measurement based on digital sampling in an intelligent substation is achieved.