Abstract: The 11# and 9# coals, exposed and mined at Pingsuo open-pit mine, occur in Ⅱ-Ⅲ intervals of the Taiyuan Formation, Upper Carboniferous. They were accumulated in environment of fan delta-1agoon and fan delta-tidal flat. The 4m thick 11# coal was formed in an environment of fan delta-tidal flat and the 15m thick 9# coal in all environment of fan deltaic plain, fan delta front and lagoon revering with deep water.