Polyacrylamide PAM is used in flooding. If the flooding PAM contains a large amount of insolubles or body impurities, it will gradually block the oil layer during polymer injection and reduce the polyacrylamide rate, thereby greatly reducing the oil displacement effect. Therefore, while improving the relative molecular weight of polyacrylamide, it is also necessary to avoid adverse factors that affect the solubility of polyacrylamide and ensure its good filterability.