Abstract: Plant fossils are collected from the Pennsylvanian Jiujuzi Formation near Shuiquan Nanshan in Aohan Qi, Inner Mongolia. Through systematic identification, a total of 18 species belonging to 12 genera, involving Sphenophyllales, Equisetales, Noeggerathiales, Filicopsida Pteridophyta and Cordaitopsida, among which Pecopteris (Asterotheca) hemlioides and Cordaites principalis are common and representative Late Paleozoic Cathaysian flora. Therefore the study area should belong to Cathaysian flora geographical region in the Pennsylvanian Subperiod. The age of the Jiujuzi Formation should be assigned to the Pennsylvanian. A large number of genuine ferns, seed ferns and Cordaites, which reflect tropical and subtropical climate, are found in the flora, indicating a wet and warm environment of subtropical-warm temperate zone with abundant rainfall.