The invention discloses an automatic floating centering hydraulic clamp holder. The automatic floating centering hydraulic clamp holder comprises a clamping assembly used for clamping a drill rod and a base fixedly matched with a drilling machine rack and used for installing the clamping assembly. The clamping assembly is installed on the base in the radial swing direction of the drill rod in a single-degree-of-freedom sliding mode, and a fixing elastic part used for fixing the clamping assembly to avoid the situation that the clamping assembly slides under the gravity effect is arranged between the base and the clamping assembly in the single-degree-of-freedom sliding direction of the clamping assembly; external force floating centering can be increased, so that the situation that abrasion on the drill rod during clamp holder centering is guaranteed through force generated by rotating of the drill rod is avoided; and meanwhile in a lateral orientation drilling machine, the clamp holder can also be centered under the effect of floating external force, so that the eccentric problem of an existing clamp holder under the gravity effect or the problem that the initial position of the clamp holder is repeatedly adjusted to ensure centering in different orientations is avoided.