Shock initiation of high explosive (HE) is very important for both the civilian and defense communities, and the hotspot mechanism has been widely recognized as the dominant regime. However, how the hotspots can generate conspicuous reaction of the surrounding bulk HE has still been a challenging topic in recent decades. In this work, using the physics of shock polarization and Yuheng Zhang equation, the shock wave-induced electrical breakdown (SWIEB) mechanism and the related chemical reaction rate equation was proposed for shock initiation of HE. It was found that the SWIEB mechanism agreed with most experimental observations on the shock initiation phenomena. As indicated by the performed experiments on the electrical breakdown of ammonia borne (NH3BH3) in this work, the electrical breakdown cannot only remarkably accelerate the reaction rate even at room temperature but also result in a reaction route different from the thermal reaction route, thereby yielding distinct reaction products. The experimental results suggested that the SWIEB may be an important and rational mechanism for the reaction of bulk HE around the hotspots. Overall, the proposed SWIEB may pave a new and reasonable way of understanding the physics of shock initiation and may help people design much safer HE in both the civilian and defense fields.