A short-time delay high-gradient pulse amplifier is formed by an isolation transformer, a rectifying circuit, an energy storage circuit, a pulse output circuit and a thyristor control circuit; the isolation transformer is connected with a power frequency alternating current power source and is connected with the rectifying circuit after isolation transformation; one output circuit of the rectifying circuit is connected with the energy storage circuit and the other circuit is connected with the thyristor control circuit; an output end of the energy storage circuit is connected with a pulse output circuit; an output end of the thyristor control circuit is connected with a thyristor control end in the pulse output circuit. According to the short-time delay high-gradient pulse amplifier, a thyristor is served as a capacitor discharging switch, a steep-sided pulse is generated by capacitor instant discharging, the steep-sided pulse generates a short-time delay high-gradient pulse is generated after being amplified through the pulse transformer, the leakage inductance and the distributed capacitance of the pulse transformer are reduced by reducing the number of turns of winding, or voltage at two ends of a charging capacitor in the energy storage circuit is improved by improving the voltage of the rectifying circuit after rectification, and the gradient of a pulse amplifier output pulse is increased.