A composite material structure forming method capable of improving the shape and dimensional accuracy inside a composite material structure. The method includes: winding a prepreg (2) around an inner jig (6); stacking a ply (8) on the prepreg (2) wound around the inner jig (6); and forming a composite material structure by providing composite outer plates (4a, 4b) on an outer periphery of the inner jig (6) on which the ply (8) is stacked and mounting divided outer jigs (9) thereon.