Abstract: The soil fertility in stands of different generations of Pinus kesiya var. langbianensis was studied with comprehensive evaluation method based on fuzzy mathematic theories by investigating into different soil nutrition factors sampled from stands of different generations of Pinus kesiya var. langbianensis in Jinggu County, Yunnan Province, where Pinus kesiya var. langbianensis tree species has been planted in a concentrative way. It was showed by the results that rotation of Pinus kesiya var. langbianensis has caused decline of soil fertility indicated by either effective or potential nutrition. It was also showed by the study that the more generation was, the faster and greater the effective and potential nutrition dropped in the soil.