Abstract: Pore-throat ratio is one of the most important microscopic physical properties of tight oil reservoir rocks and it has great effect on the remaining oil distribution and displacement pressure of reservoirs.After pore structure parameters of reservoir rocks were analyzed, such as pore-throat ratio, coordinate number, pore radius and throat radius, the theoretical relation between microscopic physical properties and macroscopic physical properties (porosity and permeability) of tight oil reservoir rocks was established by using the composite capillary model.Then, constant-rate mercury injection experiment data of 44 suites of cores taken from Chang 6 oil formation in Banqiao area were used for fitting.It is indicated that the porosity (φ) and permeability (k) of tight oil reservoir rocks are controlled by pore radius and throat radius, respectively.There is a good mathematical relationship between pore-throat ratio and φ^0.5/k^0.25.Oil displacement experiment was performed on two suites of cores whose permeabilities are close and porosities are more different.It is verified that the water displacing oil resistance in tight sandstones with higher φ^0.5/k^0.25 is higher.