The　propagation　of　small　surface　crack　in　a　shot　peening　residual　stress　field　for　Inconel　718　nickel　base　alloy　was　carried　out　in　this　paper.　Closure　of　small　surface　cracks　was　studied　by　means　of　in-situ　SEM　observation.　The　results　show　that　small　surface　cracks　have　lower　threshold　comparing　with　through-thickness　small　crack,　the　propagation　and　shape　change　of　surface　cracks　in　compressive　residual　stress　field　can　be　totally　explained　by　its,　closure　behaviour,　which　is　related　to　magnitude　and　distribution　of　the　compressive　residual　stress　field.