The invention provides a grinding machine of an internal combustion abrasive belt of a small-sized steel rail, which is provided with a rack, a transmission device of an abrasive belt, walking contour wheels and an internal combustion engine or a high-speed motor, wherein the transmission device of the abrasive belt and the walking contour wheels are installed on the rack, and the internal combustion engine or the high-speed motor is installed on the transmission device of the abrasive belt. The rack is spanned on a steel rail by a front walking contour wheel and a back walking contour wheel. The transmission device of the abrasive belt comprises a driving wheel, a driven wheel, a tensioning wheel, a tensioning device and an abrasive belt; and the abrasive belt is tightly sleeved on the driving wheel, the driven wheel and the tensioning wheel which are in triangular distribution, and is tensioned by the tensioning device connected with the tensioning wheel. A grinding depth adjustment device adopts a screw adjustment structure and comprises an adjustment hand wheel, a screw, nuts, a fixed sleeve and a guidance key. The grinding machine of the abrasive belt has simple and compact structure, good miniaturization, light weight and high repair welding efficiency and is convenient for the works department of railways to finish the on-line welding and repair welding operation of steel rails within a shorter window time.