Abstract: With regard to proceeding onsite investigation on gap size of the three species of natural forests (Larix principisrupprechtii, Picea asperata, Pinus tabulaeformis) in Guandi Mountain, as well as obtained from analyzing and researching the measured data: Stands of the three forest species are discrepancy in terms of canopy gap (CG) and expanded gap (EG) size, of which CG size mainly concentrated in range of 0—100 m2, in which the largest one was P.asperata, followed by P.tabulaeformis forest’s, while Larix principisrupprechtii’s was the smallest; EG size mainly concentrated in range of 50—100 m2, in which the largest one was P.tabulaeformis forest, followed by Picea asperata, and L.principisrupprechtii’s was the smallest. Fitting both CG and EG size and the result was of normal distribution and both logarithmic normal distribution and Weibull distribution could be fitting CG and EG size for the forest stands of the three species, whereas for fitting precision, Logarithmic normal distribution was considered the best fitting model by comparing the multiple correlation coefficient.