The invention belongs to the field of drilling machines, in particular to a coal mining drilling machine with a drill bit convenient to replace and aims at the problems that the existing drilling machines are mainly linear, the mining angle is inconvenient to adjust, the existing drilling machines are inconvenient to replace drill bits, the replacement speed is low. The coal mining drilling machine comprises a drilling machine base and a motor base arranged at the top of the drilling machine base, a flexible shaft is movably sleeved with a flexible shaft sleeve, one end of the flexible shaft sleeve is fixed on the side wall of a supporting board, a fixing sleeve is fixed to the other end of the flexible shaft sleeve, the right end of the flexible shaft extends into the fixing sleeve and isfixedly provided with a connecting shaft, the other end of the connecting shaft extends out of the fixing sleeve and is fixedly provided with a connecting base, an installing shaft is clamped to theright end of the connecting base, a drill bit base is fixed to the other end of the installing shaft, and a drill bit is installed on the drill bit base. Through ingenious addition of the flexible shaft, the drill bit part can be separated from the driving motor part, and therefore the angle of the drill bit can be conveniently adjusted without affecting operation of a driving motor.