Abstract: As an example of hot runner application for production of medical bottle caps, an inside-gating system was found to be required for the injection mold after analyzing the structure of plastic part. Therefore, an extending hot runner system was designed to solve the difficulty in the caps injection molding. The hot-half mold structure was analyzed and its technical highlights were summarized in this article. The designs of manifold, the extending nozzle and gate were described and calculated especially for power and expansion. Through the practical production, this extending hot runner system was found to improve the production yield and quality with a smooth molding process under the reasonable design.