The purpose of this article is to evaluate more details the effect of opening / closing of a fatigue crack to the electromechanical impedance (EMI) of the system "piezoelectric transducer / host structure The mentioned effect was investigated in the frequency range of 20-40 kHz and it is particularly significant to all component of the EMI and especially to the resistance PZT. It is established that the effect of opening / closing mainly affects the capacitance of PZT that due the change of piezoceramics relative permittivity under mechanical load. The result of the study is the base of some procedure of fatigue crack detecting by the EMI method. The developed model of EMI of ’host structure – PZT’ allows to solve main problems of the SHM system designing and optimizing of its parameters.