Abstract: In order to explore the internode growth regularity of bamboo culms, the stem elongation data of Phyllostachys nigra was collected and the growth curve was drawn. The stem paraffin section of Phyllostachys nigra, Herb bamboos Raddia guianensis and Olyra latifolia were made and observed under microscope. The results showed that: The plant height growth process of P. nigra showed the pattern of " slow-fast-slow” as most other woody bamboo species, and it was elongated from bottom to top. The increase in the length of internodes is closely related to the elongation of parenchyma cells in woody bamboos. The stem parenchyma cells of P. nigra differentiated in the middle and late stages of development, however, there is no differentiation of long and short parenchyma cells during the whole development process in herbaceous bamboo stems, it is consistent with some grass crops such as rice and maize.