Silicone elastomers are widely used to encapsulate power electronic devices. However, such devices may be subjected to square‐wave pulsed voltages with a high rate of change, which can create significant challenges for encapsulation insulation. In this article, the molecular vibration of silicon elastomer at the edge of pulsed electric field is studied. Firstly, the relationship between the intensity of molecular vibration and the parameters of pulsed electric field is explored. The experimental results show that the amplitude of the vibrations decreases as the pulse‐edge time increases, and it increases linearly as the pulse‐edge slope increases. Furthermore, the amplitude of the vibrations is proportional to the square of the amplitude of the pulsed electric field, and it increases as the space charge density increases. Then, the force analysis of charged molecule at the pulse edges is calculated, and the theoretical change law of molecular vibration intensity with pulse edge slope is deduced. Comparing the theoretical results with the experimental results, it is found that they are highly consistent. Finally, electrically induced mechanical stress caused by molecular vibration was shown to be an important factor in insulation failure.