In the natural coniferous-broad-mix forest of the Changbai Mountain and the Pinus koraiensis plantation of the Zhangguangcai Mountain range, 5 plots were set up, 331 Armillaria specimens were collected. Somatic incompatibility test showed that the density of Armillaria ostoyae genet was lower in the northeast forest of the Changbai Mountain, and it existed in rhizomorphs which was main dissmination mode. The main principle of prevention should be to stop the dissmination of the pathogeny-fungi in soil.