The complex pore structures of shales lead to a variety of pore fluid types. Taking the shales of Chang 7 Member of Yanchang Formation in Ordos Basin as the research object，the low-field nuclear magnetic resonance（NMR）technology was adopted，and the T2 relaxation time limits of multiple types of pore fluid in three types of shales were identified by combining centrifugal test with heat treatment test. The full pore size distribution characteristics of the target shales were quantitatively characterized. The results show that the pore structures of the target shals can be divided into three types：Ⅰ，Ⅱ，and Ⅲ，and their corresponding average pore radii and fluid accumulations decrease successively. The cutoff values of movable fluid in the three types of shale are 1.1，1.24，and 1.92 ms，respectively，while those of non-recoverable fluid are 0.2，0.3，and 0.54 ms，respectively. The movable fluid in type Ⅰ shale occurs in medium and large pores with a diameter of larger than 24.8 nm，and the average saturation is 30.5%；the non-recoverable fluid occurs in micropores with a diameter of less than 4.5 nm，and the average saturation is 35.3%. The movable fluid in type Ⅱ shale occurs in large pores with a diameter of larger than 41.9 nm，and the average saturation is 26.6%；the non-recoverable fluid occurs in micro and small pores with a diameter of less than 10.3 nm，and the average saturation is 40.7%. The movable fluid in type Ⅲ shale occurs in large pores with a diameter of larger than 93.6 nm，and the average saturation is 17.2%；the nonrecoverable fluid occurs in medium and small pores with a diameter of less than 26.3 nm，and the average saturation reaches 50.1%.