Abstract: The Sinian Dengying Formation in the Ziyang district,Sichuan contains a succession of dolostones with abundant blue-green algae.Four rock types have been distinguished.They are algaebinding dolostone,algal dolostone,dolomicrite and dolosiltite,which are arranged into subtidal subfacies,intertidal subfacies and supratidal subfacies,respectively.The additional types include dark grey and bluish grey mudstones and muddy dolostones.According to latest theory and approach to the origin of dolostones,the dolostones from the study area are interpreted to be partly primary in origin or originated from recrystallization.