The invention discloses a manufacturing method for a composite spar cap for a wind power blade. The manufacturing method comprises the following steps: 1), paving a double sided tape at the outer end of a vacuum opening of a spar cap mould; 2) paving a bottom diversion net, a lower separation film and a piece of lower demolding cloth on the spar cap mould on the inner side of the double sided tape from bottom up; 3), paving and covering mixed woven fabric, carbon fiber fabric and/or glass fiber fabric on the lower demolding cloth to form a mixed fiber preformed body; 4), paving a piece of upper demolding cloth, an upper separation film and a top diversion net on the mixed fiber preformed body from bottom up in sequence; arranging a runner in the moving direction of fibers and reserving a glue injection opening at the same time; finally, integrally covering the part from the top diversion net to the two ends of the spar cap by using a vacuum bag, and reserving a glue injection opening; 5), vacuumizing the vacuum bag; pouring epoxy resin into the vacuum bag, and then performing solidification molding. The manufacturing method is simple and easy to operate; the overall weight and the manufacturing cost of the wind power blade are reduced, the rigidity is improved, the operation process of the wind power blade is safe and reliable, and popularization and application are facilitated.