The invention provides a ship bilge keel positioning and mounting method. A bilge keel is mounted on an outer curved plate which is positioned in a bilge section. The method includes steps: S1, marking a positioning joining line on the outer plate, and marking a bilge keel mounting position line according to the positioning joining line and the bilge keel; S2, adopting a three-roll plate bending machine for linear curvature processing of the outer plate to form the outer curved plate; S3, using a moulding bed for transporting and positioning the outer curved plate; S4, mounting the bilge keel on the outer curved plate to form a combined section; S5, positioning and mounting the combined section on the bilge section according to the positioning joining line. At a bilge keel mounting stage, after completion of a large section group, curvature processing of the outer plate of the bilge section is performed before mounting of the bilge keel. A normal-posture faceup installation way of the bilge keel is optimized into a horizontal faceup installation way to lower installation difficulty. Bilge keel installation precision is optimized from rough installation to accuracy control, subsequent reworking is avoided due to angle control of the bilge keel, and the moulding bed guarantees linear precision of the outer curved plate in a placement and transport process to avoid subsequent reworking.