The effect of interlayer deformation on blister test for measuring adhesive strength was analyzed by modeling the interlayer as a Winkler foundation. Critical load for the initiation of debonding along the interface between the interlayer and an elastic thin film was obtained as a function of the adhesive strength, interlayer deformation, elastic modulus of Winkler foundation, and blister size. The critical pressure increases with increasing the elastic modulus of Winkler foundation. The propagation of debonding was discussed, and the arrest of debonding was observed for the condition of constant deflection. The results provide a rational for characterizing the effect of interlayer deformation on the measurement of adhesive strength from a blister test.