Reducing double-thread self-tapping screw

The utility model belongs to the technical field of screws, and relates to a self-tapping screw, in particular to a reducing double-thread self-tapping screw. The self-tapping screw solves the problem that in the screwing process of an existing self-tapping screw, burrs are inevitably generated at the implanting position, and consequently eversion is caused. The variable-diameter double-thread self-tapping screw comprises a pointed-end screw rod and a tool matching head connected to the end, away from the pointed end, of the pointed-end screw rod, a first thread and a second thread which are opposite in thread screwing direction are arranged on the pointed-end screw rod, the second thread is arranged at the end, close to the tool matching head, of the pointed-end screw rod, and the outer diameter of the second thread is larger than that of the first thread. The diameter of the tool matching head is gradually increased from the end close to the pointed nail rod to the end away from the pointed nail rod. The to