The invention discloses a hydraulic driving underwater drilling machine drill bit structure. The hydraulic driving underwater drilling machine drill bit structure comprises a core barrel, a straight joint, a clamp spring and a drill bit which are coaxially arranged. The drill bit is of an integrated structure which is formed by a drill bit steel body and a diamond carcass through hot pressing, the clamp spring is of an inverted circular cone elastic tubular structure which is consistent with the conicity of the inverted circular cone face, an axial opening is formed in the side wall and installed in the drill bit steel body, and an inward annular boss is arranged at the front end of the straight joint. According to the hydraulic driving underwater drilling machine drill bit structure, the structural design of the drill bit and the clamp spring is ingenious, using of the tools of the clamp spring, a clamp spring seat, a short circuit, a reamer and the like in a traditional core-taking process is simplified, in the drilling process, abrasion of the clamp spring and the clamp spring seat can be effectively slowed down, the service life is prolonged, the surface of the rock core is prevented from being damaged, in the core-taking process, the clamp spring seat extrudes the whole clamp spring inwards simultaneously, so that the clamp spring tightly clamps the rock core, the clamp sprig is effectively prevented from moving upwards along with the clamp spring seat, and therefore rock core drilling and taking can be completed with once operation.