The utility model provides a wave preventing device for a railway tanker, and relates to a tanker for transporting liquid, in particular to the wave preventing device used in the railway tanker. The wave preventing device comprises swash plates and a mounting seat, the mounting seat is fixed on the inner wall of the tanker, and the swash plates are fixed on the mounting seat. The wave preventing device is characterized in that the swash plates are evenly fixed on the two sides of the mounting seat at intervals in a fence shape, a hat top protrudes from the middle portion of each swash plate in the length direction, and hat edges are located on the two sides of the lower edge of each hat top, so that a hat-shaped structure is formed. The wave preventing device has the advantages that the hat-shaped structures of the swash plates meet the motion law of the hydromechanics so that longitudinal impact force and regurgitation force of liquid in the tanker can be effectively lowered, the defects that an existing swash plate is not even in stress under fluid impact, and overflowing of fluid is not even are effectively overcome, longitudinal impact on a sealing head of the tanker is reduced, running safety is guaranteed, and the service life of the swash plates is prolonged.