With the implementation of China′s “dual carbon” strategy, ultra/high-voltage direct current transmission system has been widely applied as an important technical means for new energy consumption. The power capacitors, as key devices for filtering and reactive power compensation, are widely used in ultra/high-voltage direct current transmission systems. However, the low-frequency vibrations and noises of power capacitors pose a serious challenge to the environmental standards of converter stations. To reduce the emission of low-frequency vibrations and noises of power capacitors, the electric field force of electric core under AC voltage is investigated for a start, and then the time/frequency domain distribution characteristics of the electric field force on electric core under both fundamental frequency voltage and higher harmonic voltage are theoretically derived. Based on this, the excitation of the electric core is used to simulate the vibration characteristics of the power capacitor under electric field force. Based on the vibration characteristics of power capacitors under electric field force, a low stiffness vibration isolation system design for noise reduction of power capacitor body is proposed, and the low-frequency vibration isolation performance of the low stiffness vibration isolator is simulated and studied. Furthermore, combined with acoustic finite element analysis, the comparative study is conducted on the low-frequency noise radiation characteristics of power capacitors are compared with and without the low stiffness vibration isolation system embedded. The results show that the proposed low stiffness vibration isolation system can effectively reduce the low- frequency noise emissions at frequencies 100 Hz, 200 Hz, 600 Hz, 700 Hz and 800 Hz in spite of 500 Hz, which indicate that the noise reduction of power capacitor body can be achieved efficiently.