Dissolution of cementite was found in the surface layer of 1.0C-1.5Cr steel plates during the process of surface mechanical attrition treatment (SMAT),and its evolution was characterized by transmission electron microscope (TEM),three-dimensional atom probe (3DAP) and M(o)ssbauer spectroscopy.The average grain size contained in the top surface of SMAT specimen was 10nm,and no diffraction ring corresponding to cementite grain was identified in the selected area election diffraction (SAED) pattern,which indicated the disappearance of cementite.3DAP analysis showed the average carbon concentration in ferrite (0.75 at%) after SMAT,which was almost 100 times higher than that in matrix (0.008 at%),which suggested cementite dissolve in the process of SMAT.The results of M(o)ssbauer spectroscopy indicated that partial cementite dissolved in the process of SMAT,the saturation of cementite dissolution is about 47%.Evolution of cementite involved three sub-stages:①inoculation stage,in the first 5 min of treated duration,cementite fraction is reduced only by 0.4%; ②dissolution stage,within the following 25 min cementite fraction significantly is reduced from 14.6% to 8.4%; ③saturation stage,when treatment exceeds 30 min,the fraction of cementite nearly remains the same.