HRB500 steel reinforced ultra-high performance concrete beams with different section sizes were tested to study size effect on shear performance. The experimental phenomena and results of ultra-high performance concrete beams were analyzed. The size effect on ductility, shear crack strength, and shear strength of beams was investigated. Besides, the applicability of the current specification formulas was compared on the basis of the obtained test data. The results show that the failure modes of beams with different cross-sectional size were all shear-compression failure. The stress redistribution capacity, deflection, stiffness, and main shear crack characteristic parameters of the beams were positively correlated with the section size. Furthermore, the displacement ductility coefficient, shear crack strength, and shear strength of beams decreased with the increase of cross-sectional dimensions, and there was an obvious size effect. Through comparison and analysis, the predicted values of the shear bearing capacity formula proposed by Chen Baochun were better.