Abstract: This article has calculated China Fir 's different starting and ending density, stand index, suitable tree age (the height of the top layer)density during its g rowing stage based on the natural thinning line, stand index, the mathem atical model and parameter of its iso-toplayer line.It can be concluded that the higher the starting and ending density and stand index are, the higher the suitable density w ill be, and vice versa.This is the fundamental changing rule of China Fir stand 's suitable density.It can be seen clearly from the above that the suitable stand density under certain forest site conditions, changes along with the different stages of the stand.Therefore, the suitable density of stand is not definite.