Taking bamboo as a 2 phase composite consisting of vascular bundles and matrix, the distribution of vascular bundles and the relationship between the tensile mechanical performance of bamboo and volume ratio of vascular bundles were studied by the microscopic image analysis and tensile mechanical test. The results show that the area of single vascular bundle increases gradually from the outer to the inner and the change trend is gentle when closing the inner of bamboo. The volume ratio of vascular bundles which increases from the inner to the outer becomes higher as the height of bamboo increases. The linear relationship between the tensile mechanical performance of bamboo and volume ratio of vascular bundles is revealed. Thus, the theoretical foundation for controllability of mechanical performance of bamboo is laid.