The No.11 coal seam of the Taiyuan Formation of Upper Carboniferous in the Pingshuo Mining District is generally characteristic of the middle-sulfur, high-ash and higher-organic sulfur, but there are great differences of the essential identifications among the coal layers, which might imply the remarkable diversification of the coal-forming micro-environments. The results show that the Ca/(Ca＋Fe), Th/U, Al/Ti, V/Zn, δEu andδCe could be used as the salinity indicators, the St,d and So,d/Sp,d respectively as the Eh and pH indicators, and the Ad, V/I and ΣREE as the water-dynamic indicators. Based on the indicators, the coal-forming micro-environments and the evolution of the seam were analyzed. It was considered that the seam was formed under the brackish to salt water micro-environments with the fluctuant transgression and the effect of the paleo-seawater on the peat swamp experienced three stages. The peat was formed in the slightly brackish to brackish micro-environment with the gradually reinforced water-dynamic condition during the first stage, in the brackish to salt water micro-environment with the rather strong water-dynamic condition during the second stage, and in the brackish micro-environment with the distinctly weakened water-dynamic condition during the third stage.