The present invention is to provide a waterproof connector having internally concealed grounding pin, which includes an outer housing having an isolation layer covered on a metal frame thereof by injection molding to form at least one grounding part exposed to a first accommodating space therein and at least one outer grounding pin exposed out of the isolation layer; an inner casing made of metal material and having at least one inner grounding pin abutted against the grounding part when the inner casing is mounted inside the outer housing; a terminal block formed by plastic integrally, having a plurality of connection terminals passing therethrough, and mounted inside the inner casing; and a waterproof glue layer watertightly filled in the rear ends of the outer housing and inner casing. Since the inner grounding pin is fully concealed inside the outer housing, the moisture can no more pass through the connector accordingly.