The reinforced concrete (RC) beams have three failure modes using large-scale finite element procedure LS-DYNA to simulate dynamic responses and failure modes of RC beams under blast loading. Holmquist-Johnson-Cook material model was used in concrete, the damage and strain rate effects were considered the kinematic hardening plasticity material model was used in reinforcing bars. With different rebar ratios and charges of weight TNT equivalent and stand-off distance were investigated and discussed. The numerical simulation can predict responses and flexure, flexure-shear and direct shear of the RC beams under different blast loading. The influence of the several factors have been identified and provided a theoretical basis for blast resistant design and retrofitting of the RC beam.