The invention provides a rack structure of a crawler underground drill rig. The rack structure comprises a rack. An overturning mechanism is installed on the rack and comprises a pair of first supporting devices movably installed at the front end of the rack. The first supporting devices can rotate relative to the rack, and the two ends of the first supporting devices are telescopic. A rotary shaft support used for installation of a mast assembly is arranged between the first supporting devices and is driven by an overturning oil cylinder. The angle of the rotary shaft support is adjusted through the overturning oil cylinder. The mast assembly comprises an auxiliary slide rail base installed on the rotary shaft support. A mast capable of sliding in the axial direction of the auxiliary slide rail base is assembled on the auxiliary slide rail base. A rotary bracket capable of sliding in the axial direction of the mast is assembled on the mast. A drill rig head is installed on the rotary bracket. According to the rack structure of the crawler underground drill rig, the angle and position of drilling operation can be adjusted within a wide range, and the universality of the drill rig is effectively improved.