The utility model relates to a novel on-line monitoring device for a current transformer, and belongs to the technical field of current transformer testing devices. The technical scheme is that the output terminal of a frequency conversion voltage generator (1) is connected with a secondary current terminal box, a first wideband current clamp (2) and a second wideband current clamp (3) are respectively arranged on two ends of the secondary current terminal box in a clamp connection manner, the output terminal of an MCU central processing unit (5) is connected with the frequency conversion voltage generator through a testing voltage signal-generator (4), the output terminals of the frequency conversion voltage generator, the first wideband current clamp and the second wideband current clamp are connected with the input terminal of the MCU central processing unit, and the MCU central processing unit comprises a filtering device and an acquisition device. Beneficial effects of the novel on-line monitoring device for the current transformer are that an internal wideband voltage generator is directly connected in parallel with a secondary load terminal box of the current transformer, open circuit risks are avoided, the novel on-line monitoring device for the current transformer is high in operability and practical value, and the detection efficiency can be substantially improved.