The invention discloses a method and a device for obtaining pulse string laser through itracavity modulation. The pulse string laser device is coaxially provided with a total reflection mirror, a pulse semiconductor side-pump module, a polarizing film, a quarter-wave plate, a modulator and an output mirror along the beam propagation direction. The method for outputting pulse string laser through the device comprises the steps as follows: 1, forming the laser resonant cavity through the total reflection mirror and output mirror; 2, the pulse semiconductor side-pump module works and the lumen modulator stops, the laser accumulates the inversion particle, no laser pulse is output; 3, the lumen modulator works for outputting pulse string laser. The pulse string laser device is high in pulse selecting efficiency, the pulse string repetition rate and pulse number can be controlled flexibly, the amplifying technology is used for the output pulse string laser for outputting the laser with high repetition rate and large pulse energy in a certain period of time.