Abstract: An analysis was made on the law of the Schima superba diameter structure in Hunan Qingshigang Forest Farm.The Weibull distribution,Normal distribution,Log-normal distribution and Gamma distribution were used for fitting stand diameter distribution and combined with X² fitting result for examination. The results showed that the Schima superba forest average DBH was 10.4cm,the span of diameter class ranked 5.1 to 37.1cm in the range 32.0cm,which mainly were small diameter class(6~12cm),the accumulating percentage was 83.7%. Among the whole distribution functions,the Weibull distribution fitting effect is best,followed by the Log-normal distribution,but the difference between the two distributions was similar,all of them can be used to predict Schima superba diameter structure.

Key words: diameter structure, Schima superba, Weibull distribution, Normal distribution, Log-normal distribution, Gamma distribution