In order to satisfy the electromagnetic compatibility standard, bulk capacitors are usually put in parallel with the input lines of airborne secondary DC/DC converters, which would result in a huge surge current and may cause system failures at the moment of powering on. Ordinary suppression methods are to put an inductor, or an NTC thermistor, or an MOSFET in series at the input of DC/DC converter, and then to turn it on very slowly with simple control mode. These methods have disadvantages of input voltage oscillation, suppression failure at high temperature, long delay time and suppression failure under the condition of fast repetitive surges. Based on MOSFET’s Miller effect, a circuit which could greatly extend the rise time for turning on MOSFET was presented. The rise rate of capacitor voltage was get slowed, so the surge current was suppressed. Simulation and actual tested results showed that the proposed circuit had achieved a startup delay time of only 10 ms. It could suppress the fast repetitive surge with a frequency up to 60 Hz. The rise rate of capacitor voltage could be adjusted easily.