Through the comprehensive analyses of core and drilling data from the researched area, the division of high-resolution sequences is conducted for the coal-bearing strata in Nantun Formation of Huhe Lake Sag : one long- term base-level cycle, six mid-term base-level cycles and sixteen short-term base level cycles, and furthermore the latter can be classified into two kinds and the middle can be divided into 3 kinds. By the means of the researches on the lithologic characteristics, sedimentary environments and coal accumulation action of the strata, three stages of coal accumulation can be detailed and moreover the coal seams of the region are mainly developed in the delta sedimentary facies belts of the braided rivers.