Abstract: Leptographium yunnanense is a blue stain phytopathogenic fungus associated with Tomicus piniperda, which can assist the beetles in overcoming the resistance of their host trees The length of phloem reaction zone induced by inoculation of blue stain fungus is often used as a measure of fungal virulence or level of tree resistance, with longer reaction zone length implying a more virulent fungus or a physiologically weaker host tree This paper reports the influence of temperature on the growth of the fungus and the resistance of its host trees( Pinus yunnanensis) The growth length of L yunnanense increases with temperature from 5 ℃ to 20 ℃, and the phloem reaction zone length also gradually increases; with temperature from 20 ℃ to 35 ℃, the growth length of the fungus gradually decreases, and the phloem reaction zone length also gradually decreases But these couldn't reflect the variation of the host trees' resistance or the fungus' virulence,they only mean that the variation of temperature has changed the competence abilities between the virulence of the fungus and the resistance of the host trees, and thus results in the variations between fungus growth length and the phloem reaction zone length.