Green　credit　regulation　may　increase　the　operating　uncertainty　and　worsen　the　financial　reporting　quality　for　pollution　intensive　firms.　Literature　mentions　that　enhanced　information　asymmetry　would　trigger　more　irrational　trading　and　lead　to　a　decrease　in　the　market　efficiency,　which　is　worth　investigating　under　green　credit　regulation.　Using　the　data　of　China＇s　A-share　listed　firms　from　2009　to　2015,　we　study　the　relationship　between　green　credit　regulation　and　market　efficiency　based　on　a　difference-in-differences　analysis.　It　finds　that　green　credit　regulation　reduces　market　efficiency　of　pollution　intensive　firms.　Mechanism　tests　show　that　policy　effects　are　more　pronounced　in　firms　with　higher　operating　uncertainty,　greater　information　asymmetry　and　stocks　with　more　irrational　traders.　This　study　not　only　contributes　to　a　deeper　understanding　of　the　impact　of　green　credit　policies　on　business　and　stock　markets　based　on　irrational　theory,　but　also　provides　valuable　guidance　for　green　finance　and　economic　development.