The invention provides a machining method of a B-shaped sleeve, solves the problems that an existing B-shaped sleeve production process is complex, the cost is high, the difficulty is large, and the installation quality is difficult to guarantee. The method comprises the following steps that 1), selecting a plate; 2), forming a strip-shaped groove in the middle of the upper surface of the plate, forming L-shaped notches parallel to the groove in the two ends of the plate; 3), machining the plate into a straight seam submerged arc welding steel tube, wherein the groove and the L-shaped notchesare distributed along the axial direction of the steel tube, the groove and the L-shaped notches are located on the inner surface of the steel tube, the inner diameter of the steel tube is matched with the outer diameter of the steel tube to be repaired; 4), machining an annular groove on the inner surface of the steel tube through an expanding device; 5), cutting the steel tube machined with theannular groove to obtain semicircular sleeves, wherein annular grooves are formed in the inner surface of the semicircular sleeves, the L-shaped notch is formed in the inner surface of one straight edge of the semicircular sleeve; and 6), machining welding grooves and truncated edges on the edges of the two straight edges of the semicircular sleeves, and matching the two semicircular sleeves to form the B-shaped sleeve.