Abstract: To investigate the bending deflection of prestressed steel-bamboo composite beams, twelve composite beams were designed and tested with loading mode, prestressing position and prestressing level as variables. Based on the assumed half-wave sine curve for the deformation distribution and taking the consideration of the influence of geometric change and prestressing camber of the beam in the loading process, a method for calculating the stress increment of prestressed strands in composite beams is established using the elastic theory. A unified formula for calculating the bending deflection of composite beams under one-point or two-point loading (prestressing) schemes is also developed. The comparison between the experimental and theoretical results indicates that: the proposed method can provide suitable estimations for the deflection of composite beams in the serviceability limit state. With the increase of the prestressing level, the equivalent bending stiffness of composite beams increases continuously, and higher equivalent bending stiffness can be obtained when two-point prestressing scheme is applied. Moreover, For the specimens with zero initial prestress, reliable pre-tightening measures should be adopted to ensure that the external prestressing strands can play an effective role.