To quantitatively express the particle and pore structures of purple mudstone, the microstructures of purple mudstone of the Matoushan group (K_2m), Lufeng group (J_1l) and Tuodian group (J_3t) in Chuxiong region, Yunnan Province were observed by the scanning electron microscope (SEM). The quantified structure information of particle and pore of mudstone was gained from the SEM image by Matlab software. The results showed that the microstructures of the Lufeng group, Matoushan group and Tuodian group were orderly expressed as honeycomb, petal shaped and granular aggregate. Structural strength of granular aggregate (J_3t) was significantly lower than petal shaped (K_2m) and honeycomb (J_1l). The sizes of particle and pore of three types of mudstone were not uniform. Uniformity of particle and pore circularity were poorer. The particle fractal dimensions of three types of mudstone followed the order of J_1l (1.74) > K_2m (1.64) > J_3t (1.34). The particle fractal dimensions showed that the small sizes of particles of J_1l were more abundant, and the big sizes of particles were less, but on the contrary, J_3t contained larger amount of big size particles and less small ones. The pore fractal dimensions followed the order of J_3t (1.88) > K_2m (1.58) > J_1l (1.35). The pore fractal dimensions showed that connectivity and uniformity of pore were better than the other two types of mudstone.