In this paper, a transmission enhanced system is proposed at 2.40 – 2.48 GHz Industrial, Scientific, and Medical (ISM) band, composed of a cavity antenna implanted inside human tissue and a impedance matching layer (IML) at skin-air interface. The cavity antenna is established on biocompatible Med 610 material based on 3D printing technology, and a shorted slot is etched on the top surface of the cavity, serving as the radiation part. Besides, to improve its transmission distance, a 3D printed IML integrated with H-shaped metal units is placed directly on the skin, therefore reducing the power reflection encountered at the air-skin interface. Simulated results show that with the introduced IML, a gain enhancement of over 5 dBi is obtained, providing a promising solution for communication enhancement for implantable applications.