The invention belongs to the technical field of composite member forming and relates to an enclosed composite member forming tool and an application method thereof. The invention is intended to overcome the defect that separate forming tooling for traditional enclosed composite members uses a great amount of positioning pins and fastening bolts; the enclosed composite member forming tool depends on base positioning and fully avoids the use of positioning fasteners, such as positioning pins and bolts, such that manufacture cost of the tool is greatly reduced, and tool manufacture cycle is shortened. A demolding process has no need for removal of bolts and positioning pins, demolding time is greatly shortened, the technical requirement on the demolding process is lowered, and production efficiency is improved. The enclosed composite member forming tool has good positioning simplicity, has very low damage repair rate, and has greatly extended service life.