The invention discloses a disposable telescopic drilling tool used for fire preventing and extinguishing grouting in an underground coal mine. A front leading drill bit comprises three wing panels, joints of the three wing panels are in hollowed-out design, three top cutting disks located at the topmost end of the front leading drill bit rotate by 15 degrees towards the same direction along the side boundaries of the three wing panels correspondingly, and the projection portions of the three top cutting disks on a plane perpendicular to the axis of a rod body are overlapped; a flat key is arranged on the surface of the front portion of an inner core in the length direction, and a key groove matched with the flat key is formed in the inner wall of a sleeve in the length direction; and the rear end of the key groove makes contact with a clamping component, and a plurality of grouting holes are formed in the sleeve and the inner core. According to the disposable telescopic drilling tool used for the fire preventing and extinguishing grouting in the underground coal mine, under the precondition that hole-drilling construction is not influenced, a grouting way is extended from dot grouting to line grouting, and thick liquid is grouted from the multiple distributed grouting holes to a drilling rod, so that the grouting quantity is increased, the hole blocking probability is lowered, and grouting efficiency is improved; and full cutting is achieved, thus, the hole forming speed is greatly increased, and the three top cutting disks share the destructive power of a rock body to a single top cutting disk, so that the situation that hole drilling is successfully conducted is guaranteed.