The invention relates to the technical field of building steel tube connection and discloses a die for welding a steel tube and a sleeve and a use method of the die for welding the steel tube and the sleeve. According to the die for welding the steel tube and the sleeve, a base is fixed to the bottom end of a supporting column, an operation platform is fixed to the top end of the supporting column, a fixed screw rod is arranged at the center of the operation platform, the fixed screw rod is detachably connected with a sleeve head, a clamp is fixed to the position over the operation platform through a supporting rod in a suspended manner, the central axis of a clamp outer ring is horizontally arranged, and a clamping portion and a self-tightening portion are arranged along the diameter of the clamp outer ring; the top end of a threaded rod of the clamping portion supports a clamping sheet in a jacking manner, the tail end of the threaded rod of the clamping portion is fixed to a clamping handle, and fixed columns are sleeved with clamping springs; the top end of a self-tightening rod of the self-tightening portion is fixed to a self-tightening clamping sheet, the tail end of the self-tightening rod is fixed to a self-tightening handle, and the self-tightening rod is sleeved with a self-tightening spring; and two limiting columns are symmetrically arranged on the two sides of the self-tightening rod located outside the clamp outer ring correspondingly and are parallel to the self-tightening rod, and the two ends of each limiting column are fixed to the clamp outer ring and the self-tightening handle correspondingly. The die for welding the steel tube and the sleeve is simple in structure and easy and convenient to operate.