The invention provides a low-permeability reservoir water flooding sweep area coefficient evaluation method and system. The method comprises the following steps: obtaining reservoir static parameters;according to the characteristics of permeability anisotropy in low permeability reservoirs, transforming the anisotropic reservoirs into equivalent isotropic reservoirs; obtaining a five-point well pattern streamline distribution model according to the equivalent isotropic reservoir and symmetry; according to the streamline distribution model of the five-point well pattern and the oil-water two-phase percolation theory, obtaining a calculation model of water flooding sweep area coefficient of a low permeability reservoir; obtaining a low permeability reservoir water flooding sweep area coefficient according to that calculation model of the low permeability reservoir water flooding sweep area coefficient and the reservoir static parameters.