The invention discloses an assembling and positioning structure of a main combustion hole bush on a flame tube. The assembling and positioning structure involves the main combustion hole bush and theflame tube, wherein a circle of hole is formed in the side surface of the flame tube, the main combustion hole bush is arranged in the hole, the main combustion hole bush is C-shaped, an inner clamping plate and an outer clamping plate of a positioning clamp clamping part are clamped on the inner wall surface and the outer wall surface of the flame tube respectively, the outer clamping plate is provided with a positioning pin extending to the hole, the width of the positioning pin is the same as the width of a C-shaped notch of the main combustion hole bush, and the axis of the positioning pinand the axis of the flame tube are located on the same plane. The self-made assembling and positioning device is simple and practical. The axial position A of the notch of the main combustion hole bush is extracted, and the axial position A of the bush notch is ensured to be perpendicular to the large-head end surface B of the part during assembly. The angle position of the main combustion hole bush notch is fixed, the assembly is stable, the assembly consistency is high, the assembly welding quality of the part is improved, and the machining quality is stabilized.