The invention discloses an ultra short light pulse generating device and method, and aims at solving the problem that stable high-quality chirping-free ultra short light pulses cannot be generated according to an ultra short generation scheme in the prior art. The ultra short light pulse generating device comprises an RF power supply module and a laser generation module, a phase modulation module,an intensity modulator, a filter, a compensation module connected successively, the RF power supply module provides RF signals for the phase modulation module and the intensity modulator, the phase modulation module cooperates with the intensity modulator to generate optical signals of an optical frequency comb with a flat top; the filter shapes a spectrum of the optical signals output by the intensity modulator; and the compensation module can remove linear chirping, and generates stable chipping-free ultra short pulses finally.