Diameter-variable PDC drill bit

The variable-diameter PDC drill bit comprises a drill bit body, a barrel, a male connector and a variable-diameter mechanism which are sequentially arranged and communicated to form a cylindrical cavity. The drill bit body is provided with movable blades and blade grooves, second guide grooves penetrating into the blade grooves in the radial direction of the drill bit body are formed in the blade grooves, and first guide grooves parallel to the drill bit body in the radial direction are formed in the inner walls of the second guide grooves. The diameter changing mechanism comprises a wedge-shaped T-shaped groove formed in the inner side of the movable blade, a wedge-shaped T-shaped block arranged in the wedge-shaped T-shaped groove and a motor driving unit arranged in the cylindrical cavity, a guide block matched with the first guide groove is arranged on the outer wall of the wedge-shaped T-shaped groove, and the guide block enters the drill bit body through the second guide groove. The motor driving unit is