The　influence　of　strain　on　the　behaviors　of　gas　molecules　over　surface　is　always　limited　by　the　relative　weak　gas　adsorption,　the　small　range　of　elastic　strain　of　adsorbents　and　the　uniform　response　of　surface　sites.　However,　the　latter　two　factors　may　be　overcome　in　two-dimensional　(2D)　materials　with　defects.　In　this　work,　we　employ　first-principles　calculations　to　investigate　the　behavior　of　a　series　of　common　gas　molecules　(CO,　CO2,　NH3,　SO2,　NO,　NO2　and　O-2)　on　defective　(S　vacancies　and　non-metal　C/N/O　doped)　MoS2　monolayers　in　both　the　2H　and　1T　＇　phases　under　biaxial　strain　(+/-　5%).　When　defects　are　introduced,　strain　can　cause　the　gas　molecules　around　the　defects　to　physically/chemically　adsorb,　desorb,　dissociate　or　even　react　with　dopant.　Meanwhile,　the　mechanical　energy　consumed　to　generate　strain　can　be　effectively　transferred　to　change　the　energy　of　adsorption/desorption/reaction　of　adsorbates　with　an　efficiency　of　at　least　15%　(if　only　adsorption　strength　is　altered)　up　to　200%　(if　reaction　is　triggered).　Subsequently,　a　number　of　interesting　phenomena　can　be　observed.　For　example,　the　doping-and-undoping　cycle　(e.g.,　the　C　doping　of　2H-MoS2　and　N　doping　of　1T　＇-MoS2　monolayers)　can　be　dynamically　controlled　by　pumping　relevant　gases　and　applying　proper　strain.　Reversible　adsorption　and　desorption　of　NH3　on　defective　MoS2　monolayers　in　both　phases　can　be　achieved　within　+/-　3%　strain.　NO　or　NO2　and　CO　can　be　converted　into　non-toxic　N2O　and　CO2　over　the　N-doped　(3%　strain)　and　O-doped　(-　3%　strain)　1T　＇-MoS2　monolayers.　In　essence,　defective　2D　materials　can　serve　as　ideal　multi-purpose　platforms　for　strain　engineering　the　behaviors　of　adsorbates.