In order to develop new and cultivable fungi isolates with biocontrol function, we performed isolation, identification and antagonism of special dark septate endophytes(DSE) from fibrous roots of Ulmus pumila by tissue isolation, morphology and ITS sequencing methods. Then the antagonism were tested by inhibition rates to the pathogens of common and important diseases such as fusarium wilt(Fusarium oxysporum f. sp. Cucumerinum), gray mold(Botrytis cinerea) and plant anthracnose(Colletotrichum gloeosporioides)by mycelial growth rate assay. The results showed that one DSE fungi(Upr105) was obtained from Ulmus pumila root. The colony was white fluffy, sparse, and light orange in the back, as the colony expanded and thickened, the back gradually became bright orange, and then turned dark brown and formed an inconspicuous “ring band” structure in the later stage on the medium, characterized by brown hyphae with a septum, showing “candida” enlarged cells in different shapes and not having sexual or asexual structure under the microscope. It was identified as Tricharina sp according to morphology and ITS sequencing, which taxonomically belonged to Tricharina, Pyronemataceae and Pezizales. The results of the antagonism test found that this isolate had different levels of inhibitory effects on the three indicating isolates, at the second day after inoculation. The inhibitory rates to B. cinerea, F. oxysporum f. sp. Cucumerinum and C. gloeosporioides were gradually increasing and reached the highest level 68.6%, 61.5% and 42.9% until the seventh days on, with average inhibitory rate respectively 52.8%, 44.5% and 22.8%. The screened isolates featured separatable, cultivate characters, with high inhibition rates to the indicative isolates. These isolates could serve as potential developable biocontrol fungus on common plant diseases.