Abstract: Jurassic continental red beds in Yanzhou mining area, Shangdong Province, contains abundant underground water, in which pore is the main water-bearing space. Combining micro-appearance observation with hydrargyrum-pressure experiments, pore types of red beds, micro-structure features and affecting factors of pore structures have been systematically studied. Main pore types of the red beds, such as interparticle soluble enlarged pore, contracted interparticle pore, gelatinous materials soluble pore, interparticle pore, and inter-crystal pore have been described in detail. Based on the data from 93 rock samples, the porosity of red bed varies from 0. 58% to 23.97% , and the average pore diameter varies from 2.3 um to 46.8 urn. Results show that different rock types have different micro-structures. The rock samples with same pore quantity may have absolutely different pore structures. The water-beating ability of the rocks can be controlled by their pore structures.