The invention relates to a hollow injection molding method. A movable plate, a movable mold, a sub-mold driving device, a sub-mold, a fixed plate, a fixed mold and an injection mechanism are involvedin the method. The method is characterized in that the movable mold, the sub-mold, and the fixed mold are closed, then an injection molding machine performs injection operation, after the injection iscompleted, mold opening is carried out until a required distance is achieved, the movable mold drives the sub-mold to be matched with the next station through the sub-mold driving device, then the mold closing action is carried out again, original separated part products are spliced together, then secondary injection is carried out, and the separated different products are injected together through plastics to complete hollow injection molding products. According to the method, certain procedures needing secondary processing, especially the hollow products which are provided with seals and need to be welded, are designed to be carried out in the molds, and the hollow plastic parts with the seal are the final finished products when leaving mold cavities, so that the product assembly quality stability and the fit tightness are improved, and the manpower and material resources and the workshop space are saved.