After　surface　mechanical　attrition　treatment　(SMAT)　for　316L　stainless　steel,　a　gradient　structure　in　its　surface　layer　with　grain　size　from　nano-scale　to　micro-scale　was　obtained.　The　samples　before　and　after　the　SMAT　were　annealed　in　vacuum　at　different　temperatures　for　different　durations,　and　the　structural　evolution　as　well　as　the　hardness　and　the　residual　stress　variations　along　the　depth　were　analyzed.　Experimental　results　show　that　when　the　annealing　temperature　is　lower　than　0.5　Tm　(Tm　is　the　melt　point),　no　obvious　change　can　be　found　for　the　grain　size　in　the　gradient　structure,　except　the　martensite　transformation　in　the　affected　layer　due　to　the　release　of　residual　stress,　and　the　hardness　distribution　along　the　depth　remains　unchanged.　When　the　annealing　temperature　is　higher　than　0.5　Tm,　recovery,　recrystallization　and　sharp　drop　of　the　residual　stress　occur　in　the　gradient　structure,　which　induce　significant　reduction　of　the　hardness　along　the　depth.　The　effect　of　annealing　duration　on　the　structure　and　property　of　the　SMAT　sample　is　less　important　comparing　with　the　annealing　temperature.