Abstract: 40 fixed experimental plots were set up in two bamboo stands in 1985, in which the two pure Phyllostachys pubescens stands were transformed from mixed stands in 1974 and 1984,and the growth observation of the new culm in the two mixed stands at different stages had been done from 1985 to 1995 so as to find out their growth dynamic.under natural fertility at different stages after they were transformed.The results were as follows: during the observed 11 years the growth of the stands can be divided into three stages of the yearly new culm and their diameter variation,i.e.,first stage occurred in the 1st year to 4th year, in which the number of yearly new culm increased about 50% more than that in the mixed stand and reached a peak (96 new culm/(600m2.year)) in the 3rd year,and the diameter of yearly new culm decreased during the period but the output of new culm increased yearly;the second stage was from the 5th to 11th year in which the mean diameter and output of new culm kept at a stable level,and the mean diameter and output in 11th year was 10% and 52% more than those in the mixed stands, respectively; the third stage was from 12th to 21st year in which both the mean diameter and the number of new Culm declined yearly and resulted in yearly decreased output, and the mean diameter in the 21st year decreased by 3.9cm and output decreased by 17% as those in the 11th year,which showed the degradation of stands occurred in the pure bamboo stands during this period.