The invention discloses a slap laser amplifier, which comprises a slap box, lamp boxes and a frame, wherein a gain medium is fixedly connected inside the slap box, each lamp box comprises xenon lamps and partition glass. The slap laser amplifier is characterized in that the slap box comprises an upper end surface, a lower end surface, an incident surface, an emergent surface and two pumping surfaces, the number of the lamp boxes is two, the lamp boxes include a first lamp box and a second lamp box, the slap box is fixedly connected to the center of the frame, the first lamp box and the second lamp box respectively face to the two pumping surfaces of the slap box, the lamp boxes are fixedly connected with the frame, and the xenon lamps of the first lamp box and the xenon lamps of the second lamp box are symmetrically arranged along a main light path direction of laser. The slap laser amplifier has the advantages of large small-signal gain coefficient and good gain uniformity.