A multi-insert cap blow-molding method for molding a hollow plastic product which is integrally formed with elongate fastening members. Each fastening member is seated in a groove defined in a lower mold. Each fastening member is composed of an elongate outer insert cap and an inner insert cap which is positioned in the outer insert cap to be separated from a bottom surface of the outer insert cap and to divide a space defined in the outer insert cap into an upper space and a lower space. A hollow parison is positioned between an upper mold and the lower mold. Hot air is blown into the parison with the upper and lower molds enclosing the parison to mold the parison and integrally fuse a portion of the parison to an inner surface of the fastening member. Then, the resultant product which is cooled, discharged and finished.