Dielectric Frequency Response (DFR) test application is one of the way spreading High Voltage bushing’s diagnostic possibilities during Service period. DFR bushing’s monitoring and statistic system are absence at present time. So it’s not possible to analyze massive results after bushing’s tests at electricity equipment. There is difficult practice question - how much kind of sensitivity method will influence on insulation condition on the future Service period? What features of the frequency response in the analysis indicate the presence of definite defects in the insulation system?