Abstract: In order to reduce the discharge spark energy of the intrinsic safety power supply, several measures are proposed in this paper. When the over-current protection occurs, DC-DC or AC-DC module should be turned off as quickly as possible, and the switching transistors of main over-current protection should avoid working in deep saturation state. It is proved to be more effective in practice that the control circuit of switching transistor performs in the state of switch on in place of switch off. In addition, it will be helpful to decrease the discharge spark energy by routing properly for the circuit board.