Abstract: Both NMR T2 spectrum and mercury injection analysis of cores can reflect characteristics of pore structure in rocks. A transformation model from T2 spectrum to pore throat radius distribution is established by using non-linear relationship. The average pore throat radius obtained from the transformation model is very close to that obtained from mercury injection analysis, which verifies the validity of the model. Based on the analysis of NMR T2 spectrum of the same low-permeability core which is saturated by oil of different viscosities, a viscosity range suitable for the transformation model from T2 spectrum to pore throat radius distribution is determined. The method overcomes the NMR’s limitation that the technology can only be used for aquifer pore structure evaluation, and realizes pore structure evaluation for oil reservoirs, providing a significant research means and theoretical basis for evaluation and reasonable development of low-permeability and low-viscosity oil reservoirs.