The invention mainly discloses a sizing machine. According to the technical scheme, the sizing machine comprises a yarn releasing device, a pre-cleaning device, a sizing mechanism, a sizing agent recovering device and a yarn withdrawing device, wherein the pre-cleaning device comprises a dust collector, the dust collector comprises a yarn inlet, a yarn outlet, dust collecting heads and an impurity box, and a yarn guiding ring is arranged inside the dust collector; the sizing mechanism comprises a sizing agent tank and sizing equipment, the sizing equipment comprises an immersing roller, a sizing roller and squeezing rollers, supports are arranged on two sides of the sizing agent tank, the squeezing rollers are movably connected onto the supports, and air cylinders are arranged on the supports and connected with the squeezing rollers; the sizing agent recovering device comprises a fixed frame, a sizing agent brush and a recovering tank; a water level sensor is arranged in the sizing agent tank, a replenishing device is arranged on one side of the sizing agent tank, and the sizing agent water level sensor is electrically connected with the replenishing device. The sizing machine is uniform in sizing and little in waste, yarn before sizing can be cleaned so as to avoid pollution of the sizing agent tank, and the sizing agent in the sizing agent tank is replenished timely.