Based　on　the　Von　Mise　yield　criterion,　the　finite　element　software　ABAQUS　was　used　to　studied　the　effect　of　thermal　shock　process　on　autofrettaged　residual　stress　in　the　ultra-high　pressure　polyethylene　reactor,　the　distribution　of　autofrettaged　residual　stress　after　thermal　shock　was　obtained,　and　the　law　and　reason　of　residual　stress　relaxation　in　autofrettaged　reactor　under　thermal　shock　were　analyzed.　The　results　showed　that　the　relaxation　of　the　residual　stress　mainly　occurred　within　2　mm　of　the　inner　wall,　and　the　relaxation　rate　of　the　inner　wall　was　the　highest;　The　superposition　of　the　thermal　stress　and　the　autofrettaged　residual　stress　caused　the　compressive　tangential　plastic　deformation　near　the　inner　wall　area,　resulted　in　the　redistribution　of　the　residual　stress　of　the　reactor.　When　the　residual　stress　relaxed　to　a　certain　value,　the　superposition　was　not　enough　to　continue　the　tangential　plastic　deformation　of　the　reactor,　then　the　residual　stress　would　not　continue　to　relax.　©　2018,　Lanzhou　Petroleum　Machinery　Research　Institute.　All　right　reserved.