The composite sandwiching block of ceramsite lightweight aggregate concrete and ordinary concrete were designed， and the interfacial bonding shear strength was tested. The final shear failure surface layer was composed of the two kinds of concrete materials and the initial casting interface with different quantity. A shear failure model for the casting bonding interlayer of the lightweight aggregate concrete and ordinary concrete was proposed， in which the multi-layer velocity discontinuity was supposed. The analytical solution for the shear strength of the casting bonding interlayer was deduced based on the Mises yielding condition and Coulomb shear failure condition. The model relates the final shear failure strength to the forming， the developing of the shear failure interface and the material properties of the concrete and the initial casting interlayer. At the same time， the analytical solution clearly indicates that the final shear failure for the composite casting of lightweight aggregate concrete and ordinary concrete follows the Mohr-Coulomb strength rule considering the influence of the casting interval time， the preparing method of the casting interface and the normal force.