Abstract: To improve the crack resistance of ordinary concrete and address issues such as large deformation and excessively wide diagonal cracks in fiber-reinforced polymer (FRP) reinforced concrete beams, glass fiber reinforced polymer-based stirrups with steel fiber reinforced concrete (GFRP-R-SFRC) beams specimens were prepared. Shear tests were conducted on these GFRP-R-SFRC beam specimens to investigate the influence of steel fiber content and shear span ratio on the distribution and width of diagonal cracks. On this basis, considering the characteristics of GFRP stirrups and the influence of steel fiber content, the calculation method for GFRP stirrup stress was modified, and a formula for calculating the maximum width of diagonal cracks in the specimens under shear was proposed. The results show that incorporating steel fibers can significantly inhibit the initiation and propagation of diagonal cracks in GFRP-R-SFRC beams, although a larger shear span ratio is not conducive to the effectiveness of steel fibers in crack suppression. Within a certain range of fiber content, under identical shear conditions, the width of diagonal cracks in GFRP-R-SFRC beams decreases with an increase in fiber content. Compared to specimens without fiber addition, the maximum width of diagonal cracks in specimens with 1.5% (volume fraction) steel fiber content was reduced by 24.3%. The calculated results of the proposed formula for the maximum width of diagonal cracks agree well with the experimental results, providing important reference for the promotion and application of GFRP-R-SFRC beams in practical engineering.