A compact,lower cost,angular multiplexing multi-pass slab amplifier is reported.The traditional rod structure has serious optical distortion,including thermal focusing,doub le focusing caused by stress,stress birefringence.The slab structure can reduce the impact of these effects,and impr ove the quality of laser beam.The slab laser geometry permits efficient use of the unsaturated gain mediu m by using angular multiplexing.Standard methods,such as polarization multiplexi ng,require the beam to be near to retrace its path.This retracing can result in feedback into the oscillator source and will,lead to par asitic oscillation of the amplifier.These problems due to retracing its path can be reduced if using angul ar multiplexing.A passively Q switched laser with repetition frequency of 20kHz,pulse duration of 2.5ns and average output power of 0.5W is used as the master oscillator.Comparing the two ways of three-pass amplificatio ns,we realize a method to effectively amplify the seed laser with nanosecond pulse duration and microjoule energy.Whe n the seed laser is totally reflected in the Nd:YVO_4slab,the average output power of 3.2W is achieved.Compared wit h other methods,this method can obviously eliminate the thermal lensing effect and enhance the output power.