The invention discloses a secondary testing device of a current transformer. The secondary testing device comprises a plurality of cable clamps respectively clamped on each terminal of the current transformer, wherein each cable clamp is welded with and is in plastic package with one end of a wire, and the other ends of the plurality of wires are connected with each other. The invention also discloses an assembly of the secondary testing device of the current transformer. The contacts of the plurality of testing lines of the secondary testing device of the current transformer are connected with each other. The secondary testing device of the current transformer has the beneficial effects that when testing is implemented, three terminals of a winding to be tested are set aside, and the clamps are respectively clamped on other terminals of the current transformer; when the winding to be tested needs replacing, the clamps clamped on the three terminals of the winding to be tested are taken down, and are respectively clamped on the three terminals of the winding tested last time, and therefore the device is simple to operate and time and labor are saved.