Based on the anatomical and chemical properties, a representative volume unit was studied to predict the longitudinal elastic modulus of bamboo (Phyllostachys glauca McClure). Microstructure features and chemical characterization of bamboo were obtained. Elastic constant of cell wall in length was derived by the application of rule of mixture. Taking advantage of the representative volume unit model, the longitudinal elastic modulus prediction formula of bamboo was established, and the theoretical and experimental value were calculated. The results showed that modified formula was acceptable to predict the longitudinal elastic modulus value with the error rate between predicted and experimental values below 25%. It is feasible to simplify the microstructure to calculate the longitudinal elastic modulus by model.