Diameter-adjustable drill bit of rotary drilling machine

The utility model provides a diameter-adjustable drill bit of a rotary drilling machine, which relates to the technical field of fender post foundation construction, and comprises a drill bit and a plurality of telescopic grooves, and a telescopic wing structure is arranged in each telescopic groove; a drill rod socket is welded to the middle of the top end of the drill bit, a drill rod is inserted into the drill rod socket, and a pressing disc is welded outside the lower end of the drill rod. Each telescopic wing structure is formed by splicing five sections of round steel columns, every two sections of round steel columns are rotationally connected through a round steel bolt, and a spring is arranged on the outer side of the joint of every two sections of round steel columns. The telescopic grooves and the telescopic wing structures are additionally arranged on the outer side of the drill bit, and the diameter of the drill bit is adjusted by bending the four telescopic wing structures under extrusion force;