Tensile　and　fracture　properties　of　X80　pipeline　steel　were　studied　in　a　mimic　petrochemical　environment.　X80　pipeline　steel　specimens　were　firstly　exposed　to　air　or　H2S　corrosive　medium.　Then　their　tensile　properties　and　delta-Delta　a　resistance　curves　were　obtained　in　experiments.　The　influence　of　H2S　corrosion　on　the　X80　pipeline　steel＇s　crack　growth　resistance　curve,　fracture　toughness,　and　plastic　work　loss　was　analyzed.　The　comparison　between　the　test　results　after　two　pretreatments　indicates　that　there　was　no　significant　difference　in　the　X80　pipeline　steel＇s　ultimate　tensile　strength　before　and　after　H2S　corrosion.　But　fracture　elongation,　area　reduction　and　fracture　toughness　varied　greatly　(a　substantial　decrease　in　elongation　and　reduction　of　area).　The　crack　growth　resistance　curve　of　the　specimen　in　air　was　obviously　higher　than　the　crack　growth　resistance　curve　of　the　corroded　one.　Under　stable　crack　growth　stage,　the　crack　initiation　toughness　delta(0.2BL)　of　the　specimen　in　air　was　0.732　mm,　2.02　times　that　of　the　corroded　one　(0.364　mm).　In　the　case　of　similar　crack　growth　Delta　a,　the　plastic　work　required　in　the　crack　growing　process　(U-P)　of　the　specimen　in　air　was　2.29　times　that　of　the　H2S-corroded　specimen　(U-P＇　).　H2S　corrosion　resulted　in　a　significant　reduction　of　the　fracture　toughness　of　X80　pipeline　steel.　Hence,　H2S　corrosion　should　be　avoided　in　the　process　of　natural　gas　transportation　by　pipelines,　so　as　to　protect　the　pipeline　steel　from　toughness　degradation.