By double-sided shear experiments on the test blocks superposed by ceramsite lightweight concrete and ordinary concrete, the influence of the surface treatments and pouring interval time on the bonding performance of the bonding surface was investigated. At the same time, the modal characteristics and formation mechanism of the microstructure on the bonding surface were analyzed using a scanning electron microscope (SEM). The results show that with the extending of the pouring interval time, the shear strength of the bonding surface diminishes under the same law for the two treatment methods. The adequate hydration reaction on the bonding surface after artificial chiseling results in denser microstructure without any distinctive microcracks or defects. With the fly-ash mortar brushed on the pouring surface, the mechanical occlusion force and effective frictional resistance is weakened to a certain extent, as well as the micro-cracks on the bonding surface. After the ordinary concrete is poured later on, micro-cracks and micro-void defects generate locally because of the weakened friction on the surface, which in turn affects the bonding performance and shearing properties of the pouring surface.