This paper considers the fracture mechanics of a ceramic foam under sudden thermal load. The ceramic foam is of semi-infinite and contains an edge crack perpendicular to its surface. The temperature field and transient thermal stress field in un-cracked medium are calculated first. Then, the stresses are used as the crack surface traction with opposite sign to formulate the mixed boundary value problem. Numerical results for the stress and stress intensity factor are calculated as the functions of the thermal shock time, the crack length and the relative density of the foam. Crack propagation behavior and the thermal shock resistance of the ceramic foam are discussed in details.