Abstract: The major stem borers Monochamus alternatus, Tomicus piniperda and Shirahoshizo insidiosus were sampled from 46 stems of wilting Pinus yunnanensis in the occurrence area of Bursaphelenchus mucronatus, and the specimens were isolated and examined by microscope. It was showed by the results that Monochamus alternatus carried Bursaphelenchus mucronatus, which was assumed the main vector insect of B. mucronatus in Yunnan Province. There were no B. mucronatus found out from specimens of Tomicus piniperda and Shirahoshizo insidiosus. The control countermeasures were put forward based on analyzing the damage characteristics of B. mucronatus in Yunnan Province.