The invention provides a novel plastic spraying gun with a preheating function. The novel plastic spraying gun comprises a plastic spraying gun body, a powder bottle, a mixing mechanism, a gas supply mechanism and a flame holder. The plastic spraying gun body comprises a gun barrel and a gun stock. A liquid storage cavity is formed in the gun barrel. The powder bottle is detachably mounted on the gun barrel. The mixing mechanism comprises an oxygen supply pipe, a spiral coil, a first communicating pipe and a second communicating pipe. The gas supply mechanism comprises a plurality of flammable gas guiding and feeding pipes and a plurality of third communicating pipes. The flame holder comprises a flame holding frame, an ignition device, a plurality of liquid storage pipes and a plurality of flow guiding pipes. The flame holding frame is detachably mounted on the gun barrel and located at gas outlets of the flammable gas guiding and feeding pipes. The ignition device is mounted on the flame holding frame. All the liquid storage pipes are mounted in the flame holding frame. The flow guiding pipes and the liquid storage pipes correspond on to one. The flow guiding pipes communicate with the liquid storage pipes and the liquid storage cavity. The novel plastic spraying gun is convenient to use, and heat generated through burning of flammable gas is effectively utilized.