The utility model discloses a polyvinyl chloride that body legal system polyvinyl chloride's combination is system of sieving in grades, this system are used for the classifying screen to divide the polymeric kettle internal reaction to generate, including feeding storehouse, first feed bin, second feed bin, first blowback filter and second blowback filter, the discharge gate of polymeric kettle and the feed inlet in feeding storehouse intercommunication, the feeding storehouse is whirlwind separator, and this whirlwind separator's upper portion has separate outlet, and the bottom has the export of subsiding, and this separate outlet communicates with the entry of first blowback filter, the export of first blowback filter and the feed inlet of first feed bin intercommunication, first feed bin also is whirlwind separator, and this whirlwind separator's upper portion also has separate outlet, and the bottom also has the export of subsiding, and this separate outlet communicates with the entry of second blowback filter, the export of second blowback filter and the feed inlet of second feed bin intercommunication, the bottom of second feed bin has the export of subsiding. This system can grade in the ejection of compact, has greatly improved hierarchical ability.