The invention discloses a water cannon preventing assembly for a ship chimney. The water cannon preventing assembly comprises water fenders; the water fenders are pivoted to one sides of smoke outlets of smoke exhaust pipes of the chimney through pivoted bases and connected with a power device through a connection rod mechanism and can swing around axes pivoted to the pivoted bases under driving of the power device, and the smoke outlets are selectively blocked by the water fenders; and the angle of the smoke outlets, inclining towards a stern, of the smoke exhaust pipes is 15-45 degrees. Compared with the prior art, the water cannon preventing assembly for the ship chimney is simple in structure, rainwater and water cannon attacking water can be effectively prevented from entering the inside of the smoke exhaust pipes, and the effect that a ship can run normally is ensured.