The utility model discloses an auxiliary tool for testing the transformation ratio of a current transformer. The device comprises a screw rod, a nut capable of being screwed on the screw rod, a sliding ring capable of sliding on the screw rod, a guide rod and a radial connecting piece, the first end of the guide rod is connected to the sliding ring; the first end of the radial connecting piece isconnected to the guide rod; the second end of the radial connecting piece is connected to the screw rod, the guide rod can rotate with the connecting point of the sliding ring as the center, the relative position of the second end of the guide rod and the screw rod is changed, and the second end of the guide rod makes contact with a female base of the current transformer by adjusting the nut and the sliding ring. When the transformation ratio of the current transformer is tested, the auxiliary tool plays a role in connecting the test cable and the female seat, and direct contact between the test cable and the female seat is avoided, so that the problems of troublesome disassembly and assembly, time consumption and easiness in poor contact or falling off when the test cable is directly connected with the female seat are solved.