Abstract: The undisturbed loess in 14 sites of typical geomorphologies in the Loess Plateau is taken as the research object. With the scanning electron microscope, loess microstructural images are obtained. By using the Pores and Cracks Analysis System (PCAS), the pore microscopic characteristics of the undisturbed loess in terms of scale, distribution, arrangement and type are gained. The fractal theory is also used to analyze the pore microscopic characteristics of the loess hilly-gully region, loess tableland and loess platform. The results show that there are significant differences in the pore structure of the undisturbed loess in different geomorphologies. The facial porosity ratio in the loess hilly-gully region is significantly greater than that in the loess tableland and loess platform. There is a negative correlation between the average pore area and pore number. The pore number decreases from west to east in the loess hilly-gully region, increases in the loess tableland, and varies greatly in the loess platform. The pore porosity fractal dimension is relatively uniform in the loess hilly-gully region, but increases from west to east in the loess tableland, and there are great differences in the loess platform. The probability entropy is mostly greater than 0.98. Pore arrangement is confusing and lacks obvious directionality. The loess tableland has the largest average form factor and the lowest pore fractal dimension. The loess tableland pore is smoother and its pore complexity is lower.