The invention relates to the field of locking devices of connectors, in particular to a step-by-step locking device for a plug of a novel electric car connector. The step-by-step locking device comprises a plug component, a socket component and a handle component, wherein a first guide post of the plug, a second guide post of the pug and a socket guide post respectively slide to the head ends of a first track, a second track and a third track in a locking state; the first guide post of the plug, the second guide post of the plug and the socket guide post respectively slide to the tail ends of the first track, the second track and the third track in an unlocking state; and when the locking state is converted into the unlocking state, particularly, the second guide post of the plug slides to the middle part from the head end of the second track, the second guide post of the plug is blocked at the upper end of an offset sub-rail, and the handle component exerts up-inclined external force, so that the second guide post of the plug moves to the lower end of the offset sub-rail, and further slides to the tail end. The step-by-step locking device has the beneficial effect that a user does not need to directly contact an outer cover of the connector when locking or unlocking the outer cover, so that the electric potential safety hazard when an electric car is charged is removed.