The invention provides an oil displacement system for a low permeability reservoir. The oil displacement system comprises an associative polymer having molecular weight of 1014000 to 9975000. The associative polymer comprises, by mole, acrylamide, 0.09-10.2% of a hydrophobic monomer and 0-15.4% of a functional monomer. In the oil displacement system, a concentration of the associative polymer is in a range of 200 to 3500 mg/L. Compared with the prior art, a small amount of the hydrophobic monomer and functional monomer are introduced into the polymer molecular chain so that the associative polymer is obtained and the hydrophobic groups are combined into a space network structure in the aqueous solution so that the viscosity of the system is greatly improved, a high resistance coefficient is built and a high residual resistance coefficient is built. Through introduction of the functional monomer into the space network structure, the system has good resistance to a temperature, a salt and shearing and good aging stability, improves an oil-water mobility ratio of low permeability reservoir, improves injection water wave and efficiency and improves the recovery of low permeability reservoir.