The factors that influence the amplification efficiency of diode end-pumped Nd∶YAG slab laser amplifier are theoretically analyzed, and a master oscillator power amplifier continuous wave laser system is designed. A narrow linewidth 1064 nm fiber laser is used as the seeder, and series and then double pass on two Nd∶YAG slab laser amplifier is followed. The two Nd∶YAG slab laser amplifiers have the same configuration, with the slab of 150.2 mm×2.5 mm×30 mm, which are pumped in double end by diode laser array (DLA). The continuous laser is output when the amplifier is pumped at 21.6 kW, with output power of 5.4 kW, optical to optical efficiency of 24.8%, and beam quality β of 3.5. Furthermore, the beam quality could be improved to 2.5 with the help of spatial filter.