Thermal shock properties of Q235A steel used ternary-boride-based (TBB) cladding material has been studied. The result indicates that this cladding material has excellent resistance to thermal shock and that the cracks are not difficult to occur at the interface of cladding layer and steel substrate. The mechanism of thermal shock failure is fatigue failure brought by cycle stresses. The thermal shock has little influence on the hardness of cladding layer. The structure of cladding layer has no obvious change after the thermal shock, but the phase of steel substrate change from ferrite and pearlite to martensite.