Based on the exhaust gas electrostatic monitoring signals of a turbo-shaft engine, an analytical study is carried out in combination with other engine operating parameters on two time scales. The results presented in this study show that both the engine operating condition and health status have a significant effect on the monitored exhaust gas electrostatic signal. On the small time scale, for an engine without fault the major factor that may cause change in the electrostatic signal is fuel delivery, and the energy of the signal will increase almost exponentially with more fuel feed. On the large time scale, given a constant fuel delivery and power shaft speed, the energy of the exhaust gas electrostatic signal will increase as the engine deteriorates gradually. The trend extracted from the monitored signal is in agreement with the theoretical analysis, which may serve as an initial basis for the establishment of a base line in the electrostatic signal, and in turn facilitate further application, such as to gas path component condition monitoring and fault identification. The research also demonstrates that the electrostatic monitoring technique can not only provide a precursor for the impending fault, but also track the gradual performance degradation for a turbo-shaft engine, and this may mean an extension of the capacity and application of the electrostatic monitoring sensor in engine health management.