A new laser amplifier structure based on Ndglass regenerative amplifier and off-axis four-pass amplifier is designed for high power laser facilities. The parasitic oscillation and pencil beam of the four pass amplifier are studied and a method is introduced to suppress them. By injecting a 1053 nm single longitudinal mode laser pulse with pulse duration of 3 ns and pulse energy of 1 nJ, a 10.3 J amplified pulse with a 2% shot-to-shot energy stability is obtained. The total gain of the amplifier system is over 1010. The output laser beam is a flat top profile with a 71% near field fill factor and modulation of 1.4 and 91% pulse energy can be focused into 2 times of diffraction limits. The experimental results and output performance of the amplifier system fully meet the requirements of the pre-amplifier of high power laser facilities, which shows that multi-pass amplifier can be used in high power laser facilities.