Heavy　haze　events　occur　frequently　over　northeast　China　during　the　winter,　despite　the　successful　implementation　of　the　Clean　Air　Act,　which　primarily　targets　fossil　fuel　sources,　in　recent　years.　Agricultural　fires　have　been　suggested　as　one　of　the　main　causes　of　these　haze　episodes.　However,　their　regional　contribution　to　fine　particulate　matter　(PM2.5)　pollution　has　not　been　systematically　evaluated.　In　this　study,　we　use　the　GEOS-Chem　model　to　investigate　the　role　of　agricultural　fires　in　heavy　haze　episodes　from　December　2018　to　March　2019　in　Heilongjiang　province.　Our　results　show　significant　discrepancies　between　the　simulated　and　observed　PM2.5　concentrations　during　severe　haze　pollution　days.　By　increasing　agricultural　fire　emissions　in　the　GFED4s　inventory　by　a　factor　of　∼23,　we　are　able　to　better　replicate　the　haze　episodes　in　the　model,　indicating　a　severe　under-representation　of　agricultural　fires　in　the　inventory.　Furthermore,　the　baseline　simulation　overestimates　the　observed　black　carbon　to　organic　carbon　ratio　in　Harbin,　suggesting　a　biased　emission　ratio　specified　in　the　inventory.　Our　assessment　underscores　that　agriculture　fires　constitute　the　main　cause　of　the　extreme　haze　episodes　during　the　study　period,　and　a　strictly　implemented　ban　would　improve　air　quality　with　substantial　health　benefits.　©　2024　American　Chemical　Society.