To investigate the influence of steel beam height ratio on the flexural performance of steel-UHPC composite beams， three composite beams with different steel beam heights were designed and fabricated， and their flexural performance was tested using a four-point loading method. The test results indicate that all specimens undergo bending failure， and they are characterized by the yielding of the entire steel beam section and the crushing of the UHPC top slab. When the steel beam height ratio is increased from 0.243 to 0.5， the ultimate bending capacity of the composite beam is improved by 48.11%. In addition， an increase of the steel beam height ratio can enhance the crack resistance performance of composite beams， specifically resulting in an increase of initial crack load and a decrease in maximum crack width. At the same time， the relative slip at the interface of the composite beam is increased by 31.3%. Based on the theory of elastic-plastic calculation， a section internal force calculation model was proposed to predict the flexural bearing capacity of steel-UHPC composite beams. The initial crack load， yield load， and ultimate load calculated by the model are basically consistent with the experimental results， which is verified that the analytical model is reliable.