The present invention relates to a pretreatment equipment capable of on-line improving yarn sizing performance for sizing machine. Said pretreatment equipment can be mounted between the warping beam frame of sizing machine and size box, and is formed from the following several portions: box body, guiding roller, high-voltage discharge heads, ozonator, UV irradiation device and sealing rubber-covered roll. Said invention also provides the working principle of said pretreatment equipment and its operation method. |