A fast impulse source with parallel-double-crystal for optical clipping is developed, which is used in laser physical experiment to chop pre-pulse. The impulse source works in a voltage-increased mode, and consists of photoelectric conversion module, high voltage supply module and switching circuit. Photoelectric conversion module transforms the optical signal to switching signal for control outputting high voltage pulse; integrated high voltage supply module and switching component simplify the circuit design, enhance the reliability; the reasonable circuit and parameter design ensure outputting satisfactory high voltage pulse steadily. The impulse source outputs negative high voltage pulse with amplitude>4 000 V, falling edge<10 ns and time jitter<1 ns, which has been successfully applied to laser physical experiment to chop pre-pulse.