The invention relates to the field of ship tools, in particular to an oval hole opening device for a ship body. The oval hole opening device for the ship body comprises a fixed seat, a guide rail rackand a rotating rod. A first guide rail and the second guide rail which are perpendicular to each other are arranged on the guide rail rack. A first guide block used for assembled on the first guide rail in a guide manner is rotationally assembled on the rotating rod. A second guide block used for assembled on the second guide rail in a guide manner is rotationally assembled at the inner end of the rotating rod. A cutting knife used for hole opening is arranged at the outer end of the rotating rod. The second guide block and the first guide block are arranged in a spaced manner. The second guide block and the cutting knife are movably assembled on the rotating rod in the axial direction of the rotating rod. A vacuum suction cup used for adsorbing to the ship body is further arranged at thebottom of the fixed seat. The vacuum suction cup is arranged at the bottom of the fixed seat and is suitable for various materials, the oval hole opening device can be firmly fixed to ship bodies ofdifferent materials through vacuum pressure, and the lineation precision and cutting effect of oval holes are guaranteed.