The causation of the generation of strong amplified spontaneous emission (ASE) in the Nd∶YAG slab is analyzed, and the academic and experimental researches on suppressing ASE in high gain laser slab are developed. The pumping duty ratio is 8%, the peak pumping power is 21.38 kW and the injecting intensity of 1064 nm continuous detecting laser is 4 W/cm 2. The output power amplifying ratios of the detecting laser are 1.82 and 1.92 respectively with common evanescent coating and multilayer coating. The total stored energy in the slab increases by 4.6%. The experimental results show that ASE effect can be suppressed and the total stored energy in the laser slab can increase to a certain extent when special multilayer coating is coated on the top and bottom surfaces of the slab.