The invention discloses a polishing device for marine metal castings, comprising: a frame, a shaping mechanism, a double-sided sand opening mechanism, a polishing mechanism, a detection mechanism for testing the polishing quality, a turning mechanism, a limit device and a control mechanism , the shaping mechanism is set at the front end of the frame, the double-sided sand-opening mechanism is set at the rear of the shaping mechanism, the polishing mechanism is set at the end of the double-sided sand-opening mechanism, the detection mechanism is set at the rear of the polishing mechanism, and the turning mechanism is set at the detection mechanism At the rear, the limit device is set on the corresponding workbench under the polishing mechanism, and the shaping mechanism, double-sided sand opening mechanism, polishing mechanism, detection mechanism, turning mechanism and limit device are all connected with the control mechanism. In the present invention, the casting is first reshaped by setting the shaping mechanism, and then the casting is sanded by the sand opening mechanism, and the casting after the sand opening is polished by the polishing mechanism, and a turning mechanism is also provided to allow it to be processed. The product is turned over, which greatly improves its work efficiency.