The reservoir of Yanchang Formation in the southwest Ordos Basin is one of the typical tight sandstone reservoirs in China. The classification and evaluation of tight sandstone reservoir of Yanchang Formation in central Ordos Basin has attracted the attention of petroleum enterprises. In order to rationally and efficiently develop the Chang 8₁ tight sandstone reservoir in Ordos Basin, it is urgent to carry out reservoir classification and accurately evaluate the reservoir. Taking the Chang 8₁ tight sandstone reservoir in Wuqi area as an example, the fractal dimension of the target layer was calculated by NMR experimental data, and the micro-pore structure of the Chang 8₁ tight sandstone reservoir was quantitatively studied by combining the experimental data such as cast thin slice and scanning electron microscope. At the same time, the relationship between reservoir fractal dimension and reservoir physical properties was analyzed, and the fractal theory based on nuclear magnetic resonance experiment was used to classify and evaluate tight sandstone reservoirs. The results show that the rock type of Chang 8₁ tight sandstone reservoir in Wuqi area is mainly lithic feldspar sandstone, and the pore structure is mainly intergranular dissolved pores and feldspar dissolved pores. According to the T₂ spectral curve and fractal dimension method, reservoirs are divided into three categories. Each type of reservoir corresponds to the relevant fractal dimension, and the fractal dimension has a good correlation with the physical property parameters, which characterize the complexity of the reservoir pore structure. Combining nuclear magnetic resonance experiment with fractal dimension method to quantitatively characterize the microscopic characteristics of tight sandstone reservoir can improve the accuracy of reservoir classification.