High repetition frequency and high energy sub nanosecond solid state lasers have the characteristics of high repetition frequency,large single pulse energy and high peak power,which have a wide application prospect in the fields of national defense,military industry and industrial processing.In this paper,a sub nanosecond laser amplifier based on slab multi pass amplification is proposed.The seed light is a fundamental mode laser with a repetition frequency of 1 kHz,an average power of 4.5 W,a pulse width of 700 ps and a wavelength of 1064 nm.Then,the laser beam is shaped to match the caliber of the slab amplifier.The amplification stage adopts angle multiplexing and polarization transformation to achieve four way amplification.Finally,a sub nanosecond laser output with a frequency of 1 kHz,a single pulse energy of 189 mJ,a pulse width of 720 ps and a beam mass of 2 times the diffraction limit is achieved.