The pore structure is an important characteristic of loess that helps distinguish it from other soil types. The macroscopic mechanical behaviors of loess, such as its collapsibility and seismic subsidence, are closely related to its pore structure. In this paper, we develop a method combining Matlab and Image-Pro Plus (IPP) software to pre-process images of the loess microstructure. Qualitative and quantitative analyses of intact loess samples taken from Xining in Qinghai, Yongdeng, and Lanzhou in Gansu, Xiji in Ningxia, and Ruicheng in Shanxi are also performed at the microscopic level. Microstructural image processing is introduced, and a new method to determine three-dimensional porosity based on gray scale calculation is proposed. Results indicate that the microstructure of the Q₃ loess in different regions is closely related to the regional, depth, and climatic conditions. In qualitative analytical tests, loess particles in the area near and esat of Liupan Mountain were given priority to with grains and grume because of its rich rainwater. The climate in the western region of Liupan Mountain significantly differs from that in the east; specifically, the western region is more arid and shows a smaller contact area between particles and tendency to form trellis pores. In the test of quantitative analysis, the large pore content increases gradually from northwest to southeast in the space. Particles move closer to each other, and the distance between grains decreases with increasing depth from top to bottom; thus, the large pore content is gradually reduced. In-situ stress gradually increases, and loess particles and pores appear to rotate and deform because of squeezing with increasing of stratum depth. The elliptical ratio of medium and large pores decreases, and macropores change significantly. The soil is remodeled, and an orderly pore arrangement is achieved. Pore size and area are relatively uniform in each region, fractal dimensions and probability entropies decrease, and the rose curve is gradually smoothened.