Ultra-high performance concrete (UHPC) has been gradually used in structure engineering due to its excellent mechanical performance, however, predicting the shear capacity of the UHPC beams is still a challenge, especially for the beams with small shear span to depth ratios. To address this issue, this paper devotes to developing a rational model to predict the shear capacity of the UHPC beams with stirrups based on the modified compression field theory (MCFT) and plastic theory. The shear force will be balanced by the stirrups, matrix, fibers and shear compression zone. The contribution of stirrups, matrix and fibers on shear capacity can be predicted by MCFT, and the contribution of compression zone is determined based on plastic theory. 12 UHPC beams was designed and tested to validate the proposed model. It can be found that the predictions agree well with test results, while the current design codes, including SETRA-AFGC and SIA, give overly conservative values for UHPC beams when the shear to span is less than 2.5.