Abstract: To get some knowledge about the relationship between soil biological properties and thickress-growth of bamboo,23 plots with different productivity were selected for investigating eye-high diameter(D.E.H.) and analyzing soil samples.D.E.H. has a close relationship with the number of soil bacteria(X₁),actinomyces(X₂),fungi(X₃),activities of hydrogen peroxidase(X₄),urease(X₅),protease(X₆), and phosphatase(X₇),with correlation coefficients at 0.941^**,0.432^*, 0.682^**,0.751^**,0.768^**,0.899^** and 0.914^**,respectively.Sucrase activity(X₈) is not well related to D.E.H.The mulitiple liner regression equation is:y=2.3064+8.8954?10^-7X₁+1.8356?10^-7X₂+6.8422?10 -6X₃- 0.6099X₄-1.101X₅+6.225X₆+0.05088X₇+0.0571X₈.The multiple correlation coefficient (R=0.96) reached significent level(a=0.001).For fractional correlation coefficients,only bacteria number and protease activity (0.591 and 0.442) reached an evident level. It indicates that bacteria number and protease activity are the major factors to affect thickness-growth of bamboo.The stepwise regression equation,y=4.2026+8.827?10 ^-7X₁+7.368X₆ with multiple correlation coefficient 0.9596 and fractional correlation coefficients r(y,X₁)=0.7676,r(y,X₆)=0.5569,makes further support to the above result deduced from multiple linear regression.The 23 plots can be divided into three types by cluster analysis according to soil biological properties:high-yield,middle-yield and low-yield with the percentage of 34.8,47.8 and 17.4,respectively.The average D.E.H is 10.6,9.1 and 6.6 centmeters, respectively.

Key words: Robinia pseudoacacia plantation, carbon and nitrogen storage, allocation pattern, forest-age.