The basic mechanism of diagnosing the regional damage and the probability damage diagnosis method are studied for metal and non-metal structures. Firstly，the characteristic parameter of the structure-sensor electromechanical impedance spectrum is extracted based on the principle of electromechanical coupling. The sparse sensing array is used to obtain the correspondence between the cumulative degree of damage and the characteristic parameter. Secondly， a Gaussian probability diagnosis model for the cumulative degree of damage is conducted. With a few sensors， the damage area and the cumulative degree can be determined. The experimental results shows that the damage characteristic parameter significantly changes with the propagation of the damage. The damage area and the cumulative degree of damage can be detected well.