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In order to quantitatively characterize the porosity of tight cores, the porosity, permeability and pore size distribution of tight cores can be measured by nuclear magnetic resonance (NMR) using the proportional relationship between TT2 relaxation time and pore radius, and the free fluid and bound fluid in pores can be distinguished by TT2 cut-off value. Based on the principle of core porosity characterization by NMR, the relationship between TT2 and core porosity, permeability, pore size distribution and movable fluid in pore is discussed. Through above principles and examples, the accuracy and applicability of the NMR in the quantitative characterization of porosity and permeability of tight cores are verified. The cut-off values and pore size distribution tests of the experimental cores show that the cut-off value of core 1 is 21.85 ms and that of core 2 is 40.11 ms. Core 1 has a large small pore fraction and core 2 has a more uniform pore distribution. The results show that the cut-off values of T2 obtained by regional method are not fully suitable to the case of tight core, and it is necessary to establish a regional version of the cut-off variation range chart. [ABSTRACT FROM AUTHOR]