A series of experiments was carried out to study the matching relationship between the pore structure in the reservoir and the molecular radius of gyration. The hydrodynamic radius Dh (molecular coil dimension) was tested by dynamic light scattering and was be used to characterize the crimping degree of polymer chains and molecular coil dimension. The storage modulus and loss modulus were studied through creep recovery. CT scan was used to measure the parameters of pore throat structure in the reservoir. Finally, a polymer injection experiment has been carried out to evaluate the adaptability of polymer molecular coil dimension in the pore structure of the reservoir. Comparing pore radius with the molecular radius of gyration, it was shown that the storage modulus ratio is the key critical factor of oil displacement efficiency and its value is in the range of 10-20. It was also shown that the optimal stable pressure gradient is in the range of 0.05-0.3 MPa/s; a medium stable pressure gradient of 0.3-0.6 MPa/s is acceptable; and a stable pressure gradient above 0.6 MPa/s or no stable pressure gradient is poor. Greater molecular weight and higher concentration of polymer in the core with low permeability do not provide stable pressure.