Microscopic pore throat structure is the key focus and challenge of tight sandstone reservoir research.Regarding the Chang 6 tight sandstone in the Jiyuan area of the Ordos Basin,casting thin sections,scanning electron microscopy,and constant rate mercury injection experiments were used,and fractal theory was introduced to study its pore throat characteristics.The study shows that the pore throat of tight sandstone can be divided into two types:large⁃scale and small⁃scale.The large⁃scale pore throats are mainly dissolution pores,composite pores and curved lamellar throats.The pore throat has large storage space,obvious pore throat deformation,strong heterogeneity and large fractal dimension.The small⁃scale pore throats are strongly compacted and cemented, and mainly consist of intergranular pores,intercrystalline pores and necked throats with little deformation of pore⁃throat space,weak heterogeneity and small fractal dimension.There is a good positive correlation between the fractal dimension and the effective reservoir space.The better the reservoir is,the stronger the heterogeneity will be,and the larger the fractal dimension will be.There is also a good correlation between the fractal dimension and the pore throat structure parameter.The pore throat distribution is uneven,the connectivity is poor,the larger the fractal dimension will be.The mass fraction of clay minerals is an important factor affecting the fractal dimension of pore throat,which in turn reflects the quality and pore throat characteristics of reservoirs.