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 90 mm and 120 mm making the spans of 3 000 mm and 3 600 mm were subjected to bending collapse tests. And the load-displacement curves, initial bending stiffness, ultimate bearing capacity, deflection and failure modes were analyzed. The height of compressive zone and edge stress of tensile zone of the raw bamboo beams were 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 Phyllostachys pubescents beam conforms to the assumption of flat section, while under the condition of large deflection, the height of compression zone of section moves up, and the calculated tensile stress of failure edge is inconsistent with the calculated result of the assumption of flat section. It is suggested that the bending moment of Phyllostachys pubescents beam should be calculated according to the maximum compressive strength of the upper edge along the grain.