Abstract: Compared with ordinary partially hydrolyzed polyac-rylamide, hydrophobic associated polymer has higher capability of viscosifying action, high - temperature resistance and salt tolerance and better effects of oil displacement and profile control. In order to further improve the ability of oil displacement and profile control, study on weak crosslinked system of hydrophobic associated poly-mer(AP-P4)is carried out in laboratory. This paper introduces formula optimization of AP - P4 weak crosslinked system, discusses various factors that influence the performance of crosslinked system, and selects an optimum formula for crosslinked system.