The invention discloses a clamp used for water cutting of a side frame casting of a railway wagon and relates to a clamp. A channel for cutting liquid metal is needed for a feeder head of an existing side frame casting after the casting is finished. Harm is great and the environment is polluted when the feeder head of the side frame casting is cut through a traditional method. Although the defect of the traditional method is overcome by cutting through a high-pressure water jet technique, the side frame casting can not be located stably in a water tank. According to the clamp, the top face of a support base is a three-nail locating face C' matched with the bottom face locating face C of the side frame casting, one side face of a first locating block is two-locating-nail locating face A' matched with the middle side face locating face A of the side frame casting, and the end face, close to a second locating block, of the first locating block is a single-nail locating face B' matched with the middle bottom face locating face B of the side frame casting. A top face D' supporting a flange in an auxiliary mode is matched with the top bottom face D of the side frame casting. The gap between the second locating block and a connection rod is matched with the bottom clamping face E of the side frame casting. The clamp is suitable for the process of cutting of the side frame casting.