Abstract: The fine root morphology of different order roots and the fine root biomass of the Platycladus orientalis plantations treated with different thinning intensity and frequency were analyzed. The results showed that the different thinning measures had significant impacts on fine root biomass of the plantation, and also on the diameter, length and the specific root length (SRL) of the fine root under different root orders. Both of the thinning intensity and thinning frequency had significant influence on the fine root biomass. Compared with the control plots, the thinning intensity significantly affected the mean diameter of the 5th order roots, the mean length of the 4th to 5th order roots and the mean SRL of 3rd to 4th order roots in surface soil layer, and the mean SRL of the 2nd to 4th order roots in the subsurface soil layer. Whereas the thinning frequency significantly influenced the mean length of the 1st and 2nd order roots, the mean SRL of the 2nd to 3rd order roots in surface soil layer, and the mean diameter of the 5th order root in the subsurface soil layer.