Abstract: The effect of different cooling type after rolling on microstructure, grain size and the impact properties of 10Ni3MnCuAl rolling flat steel were studied by OM,SEM and impact experimenter. The result show that,the microstructure of water cooling type after rolling was mainly lath martensite, the microstructure of air cooling type after rolling was mainly granular bainite. The uniform and fine martensite structure after water cooling was acquired, granular bainite after air cooling was relatively thick. The impact value of water cooling type was reached 19.6-30.5 J, 2-3 times higher than the value of air cooling type,hardness increase about 2.5 HRC at the same time. The microstructure, grain size and the impact properties of 10Ni3MnCuAl rolling flat steel after water cooling were better than air cooling type.