Abstract: Pure bend sandwich beam specimen plays an important part in evaluating the fracture resistance of interface. The explicit solution of the strain energy release rate of crack propagation along the pure bend sandwich beam specimen has been deduced in the paper by use of the superposition principle of the energy and section inversion method. Based on the critical load of crack propagation along the interface through the testing measurement, the fracture toughness of four point bending Si₃N4_{/Al/Si3N4 specimens along Si3N 4/Al diffusion joining interface has been obtained by using the explicit solution.}