Abstract: The microscopic structure of 10 Pinus yunnanensis population needles, sampled from the south-east, mid -part and north -west of Yunnan plateau,were extensively investigated, observed and analyzed according to the principle and method of ecology and comparative anatomy.The morphological diversity and ecological adaptability were analyzed combined with the meteorological factors.The structure feature of P.yunnanensis needles presented polymorphism andminiaturization from south -east, mid -part to north -west of Yunnan plateau.The Casparin stripe appeared on the endodermis of the needles of P.yunnanensis (distributed in south-east of Yunnan), especially obviously in the P.yunnanensis var.tenuifolia and P.kesiya var.langbianensis distributed in the humid and hot habitats.No Casparian stripe of the endodermis of the needles was observed in Pinus yunnanensis distributed in the north -west and mid-part of Yunnan.The long term adaptation and evolution molded the relative steadiness of the needle morphology and structure.The diversity of needle morphology and structure was obvious as a result of the ecological adaptation under the complicated geographical and ecological environment.