To obtain a more accurate method for analyzing the crack width in negative moment regions of steel-concrete composite beams, a numerical calculation model of crack width under static loading based on bond-slip theory was established, considering the bond-slip relationship between reinforcement and concrete, the slip effect between steel beam and concrete slab, concrete shrinkage strain, and tension-stiffening effect. The predicted values of the model were compared with related literature data and the calculation results of standard formulas. Results show that the calculated values of the proposed model could well simulate the development process of crack width before the composite beam reached the yield load. The suggested model appeared to provide unreliable predictions that the crack width increased by 10% when the slip effect at the beam-slab interface was not considered. Compared with the experimental values, the results obtained from the standard formulas had a large deviation. While the results obtained from the proposed numerical calculation model were in good agreement with the measured values, and the dispersion coefficient was the minimum, which verified the accuracy and applicability of the model.