According to the lithological assemblages and elemental geochemistry of the measured profile，the authors studied the sedimentary and tectonic environment of the Late Carboniferous Tangjiatun Formation in Acheng． The results show that the trace elements of mudstone samples from Tangjiatun Formation have the char- acteristics of high Th，V and Cu，but low Ba，Nb and Sr． The rare earth elements are characterized by signifi- cantly light and heavy rare earth elements differentiation，relative enrichment of light rare earth elements，and a negative anomaly of δEu． The Tangjiatun Formation belongs to a marine and delta sedimentary environment， and its tectonic setting is considered as a continental island arc environment．