The invention discloses a low-permeability sandstone reservoir pore structure quantitative inversion method based on nuclear magnetic resonance. The method comprises the following steps: I, selecting a basic sample; II, classifying the type of a pore structure; III, establishing a well logging chart for identifying the pore structure; IV, establishing a pore throat distribution inversion formula according to the type of the pore structure; V, verifying the accuracy of the formula; VI, identifying the type of the pore structure of a shaft section by utilizing the well logging chart; VII, quantitatively inverting the distribution of free fluid pore throats by utilizing a nuclear magnetic resonance well logging T2 spectrum. The method has the following beneficial effects: a reliable method and technology are provided for quantitatively evaluating the pore structure, and the research concept of the current method can be broken through. The continuous free fluid pore throat distribution can be inverted by virtue of the nuclear magnetic resonance well logging, so that direct evidence is provided for evaluating the effectiveness of the low-permeability sandstone reservoir, application of the well logging information in the quantitative inversion of the micro pore structure of the reservoir is favorably explored, and the application and development of the nuclear magnetic well logging technology can be promoted.