Abstract：Three indices (uniform angle index, mingling index and neighborhood comparison ratio) are used to describe and compare the spatial structure of the natural mixed forest undisturbed by human activities and the semi-natural mixed stand of larch (Larix olgensis)-spruce(Picea jazoensis)-fir(Abies nephrolepis) which only exists in the over-logged forest of Changbai Mountains. Results indicate that two stands have the same uniform angle index of 0.52, with tree distribution being clustered. The average mingling index of the semi-natural mixed forest of larch-spruce-fir is 0.64, with moderate mixed characteristics; the coniferous trees (esp. spruce) in the stand are dominant as seen from the neighborhood comparison ratio based on Diameter at Breast Height (DBH), while the Korean pine(Pinus koraiensis) is in polarization and inferior position. The average mingling index of the natural mixed forest is 0.83 and higher than that of the semi-natural mixed forest of larch-spruce-fir, with intense mixed characteristics and higher stability; hardwood trees in the stand are dominant as seen from the neighborhood comparison ratio based on DBH, while the coniferous trees are in inferior position except spruce. The results could be used to optimize the spatial structure and near natural management of the over-logged forests and plantations.