In order to study the mechanical properties of steel-bamboo combination I-beams under long-term load， thickness of bamboo plywood， thickness of steel plate， and steel content were set as the main parameters to design two sets of 12 specimens. One group was subjected to a bending failure test after a one-year long-term load， and the other was directly subjected to a short-term bending test. The long-term effects of load on the ultimate bearing capacity attenuation， deflection， component ductility， and section strain of combination beams were studied. The deflection of combination beams at failure was calculated and analyzed based on the effective moment of inertia method. The results show that the failure test phenomenon of combination beams is related to the steel content， which is generally manifested as debonding and cracking of the lower flange bamboo plywood. The damage range of the combination beams gradually spread upward as the steel content increased. Ductility of combination beams changed after long-term loading. The effect on the combination beams is basically the same after long-term tension and compression of bamboo plywood， and the position of the neutral axis of combination beams remaines unchanged. The degree of bearing capacity attenuation is related to the thickness of bamboo plywood， steel plate thickness， and steel content. The calculated values obtained from the deflection calculation formula agree well with the experimental values， and the errors are all within 10%.