The invention belongs to the technical field of transformer bushing insulation state online monitoring and particularly relates to a transformer bushing insulation state online monitoring device and method. The device comprises a current sensing unit, a signal conditioning unit, a data acquisition and processing unit, a communication unit, a storage unit, a display unit and a power unit. The device can completely meet the measurement requirement of an intelligent substation without introduction of PT reference for calculation and is simple in installation and outstanding in economic benefit. By means of the method, the change tendency of a bushing relative to dielectric loss factor can be monitored under the situation that a voltage transformer secondary signal is not needed to be led out, accordingly an insulation state of the bushing is accurately and effectively reflected, and safe and stable running of equipment is ensured. In addition, the stipulations of an IEC61850 agreement are met, the device has a specified function and a communication model, integration of functions of the online monitoring device and a main IED can be achieved, and the transformer bushing insulation state online monitoring device and method can be applied to the intelligent substation.