The invention belongs to the technical field of cotton yarn processing, particularly relates to a cotton yarn processing slasher, and aims to solve the problem of low sizing efficiency of an existingyarn. The technical scheme includes that the slasher comprises a frame, a first guide roller, a second guide roller, a third guide roller, a squeezing roller component and a fourth guide roller, a yarn unwinding device and a yarn winding device are arranged on two sides of the frame, a squeezing device, a drying box and a heating box are arranged on a mounting plate on the frame, the drying box iscommunicated with the heating box through an air supply device, a sizing box storing slurry is arranged on the frame, yarns are outputted by the yarn unwinding device, sequentially pass the first guide roller, the second guide roller, third guide roller and the squeezing roller component and are soaked into the slurry, the yarns are squeezed by the squeezing device, and the squeezed yarns penetrate the drying box, pass the fourth guide roller and are wound on the yarn winding device. According to the slasher, the yarns can be rapidly conveyed, sized, dried and wound, so that the sizing efficiency of the yarns is improved.