The bark-beetles and ophiostomatoid fungi formed a stable association relationship in nature. It is a universal ecology phenomenon occurring frequently in forest ecological systems. The association between the beetles and fungi are regarded to some extent as a symbiosis in a broad sense. They have been extensively and intensively documented and illustrated from all over the world since it was first realized. Some research showed that Ips beetles spread over Eurasia were extensively associated with a number of ophiostomatoid fungi species. Among which, some species are important pathogens of conifers. Although the morphology and ecology characteristics of three Ips beetles, I. typographus, I. cembrae, and I. subelongatus were almost identical, these beetles were evidenced in a series studies as distinct species based on the phylogenetic analysis of DNA information and critical morphological comparison. In parallel, an ophiostomatoid fungus, Ceratocystis polonica previously recognized as a closely associated fungus with these beetles was also separated into three distinct entities resided in the Ceratocystis coerulescens species complex, and stably associated with three kinds of bark beetles, respectively, where a species specific association between bark beetles and ophiostomatoid fungi was established. The species specific association was understood as a result of co-evolution in forests where both partners lived together in a common habitat. The samples collected in this study from three allopatric Larix hosts which Ips subelongatus attacked seriously. The ophiostomatoid strains were isolated from the body surface of Ips subelongatus, blue-stain tissue or the galleries bark-beetles attacked. Observations of the colony, physiology and morphology characteristic, and comparisons of anamorph and teleomorph structures of all Ceratocystis strains, confirmed that the strains are indistinguishable from Ceratocystis fujiensis M.J.Wingf. The phylogenetic analysis based on sequences derived from the ITS regions of the rDNA operon, the partial β-tubulin gene and the MAT-2 HMG box gene, further determined a total of nineteen fungal strains as species Ceratocystis fujiensis. The study first determined Ceratocystis fujiensis extensively existed in three allopatric larch forests in northeast and north China, which formed a stable association relationship with Ips subelongatus under such ecological conditions. Ceratocystis fujiensis was proved as a dominant fungus associated with Ips subelongatus in Japan, and a pioneer species and the strongest pathogenic fungus in all the bark-beetles associated fungi. Because C. fujiensis widely infesting Larix spp. plants in China, inevitably, this phenomenon should be paid high attention. The study provides scientific basis to make the policies and measures for the government to prevent and control the composite damages of diseases and pests effectively. The result in this paper provides support to the hypothesis of species specific association between Ips beetles and ophiostomatoid fungi. Meanwhile, the multi-gene sequences characteristic indicates that I. subelongatus and C. fujiensis exist significant genetic diversity in different geographic populations, which probably predict the possibility of the species specific association occurred under species levels. The associations between Ips beetles and ophiostomatoid fungi exhibit an ideal insight into completely understanding the symbiotic relationship between the bark beetles and ophiostomatoid fungi, and species specific association as well.