In order to study the flexural performance of bamboo member, 40 groups of bamboo standard wood strips from 10 raw bamboos were tested to obtain their failure modes and flexural strength. Then, the 24 raw bamboo beams with diameters of 90mm and 120mm making the spans of 3000mm and 3600mm were subjected to bending collapse tests. And the failure modes, load-displacement curves, initial bending stiffness, ultimate bearing capacity and deflection were analyzed. The height of compressive zone and edge stress of tensile zone of the raw bamboo beams are deduced theoretically. The results show that the influence of span change on deflection of bamboo beam is greater than that of diameter at breast height. The larger diameter at breast height and the smaller span, the greater the initial bending stiffness of the bamboo beams. According to the test data and the classical elastic theory, it is calculated that the compressive zone height of the bamboo beam is about 3R/2 height of the cross-section. Under the condition of small deflection, the bending of the bamboo beam is agreement with the assumption of flat section, while under the condition of large deflection, the compressive zone height of the section moves up and no longer conforms to the assumption of flat section.