A novel macro-monomer allyl-capped octylphenoxy poly(ethylene oxide) (APE, degree of polymerization is 20) was synthesized. Then a salt-tolerant tetra-polymer (PSA) was synthesized with APE, acrylamide (AM), sodium 2-acrylamido-2-methylpropane sulphonate (NaAMPS), and vinyl biphenyl (VP). This aimed at solving a problem that oil-flooding polymers can not be applied in the oil reservoirs with high salinities. This polymer displays the excellent thickening property induced by salt, and the critical association concentration is only 0.3 g/L in 70.0 g/L NaCl; as the NaCl concentration is higher than 40.0 g/L, the apparent viscosities are much higher than those in water and rises sharply with increasing NaCl concentration. The ultraviolet spectral analysis using pyrene as probe and atomic force microscope results show that polymer chains are expanded in water and the chain bundles are formed through the intermolecular hydrophobic associations, and that the intermolecular associations are strengthened obviously in the brine solutions with high salinities and the solution viscosities increase dramatically.