Volatile　organic　compounds　(VOCs)　play　a　key　role　in　air　pollution　of　China.　Among　various　sources,　petrochemical　industry　is　one　of　the　important　contributors,　but　its　VOC　emission　estimate　still　exists　a　big　uncertainty.　Therefore,　this　study　developed　an　inverse-dispersion　calculation　method　(IDM),　and　applied　it　in　a　typical　petrochemical　plant　that　manufactures　ethylene　(170　kt/year),　polyethylene　(100　kt/year),　and　polypropylene　(61　kt/year),　and　determined　the　VOC　emission　amount　for　this　complex　industrial　area　source.　Firstly,　this　study　monitored　VOC　concentrations　around　this　plant　in　April　of　2017,　and　found　that　the　VOCs　at　downwind　receptors　was　obviously　higher　than　the　level　at　background,　higher　by　20.7　ppb　on　average.　This　VOC　increment　was　mainly　contributed　by　ethylene　(30.4%),　propylene　(17.8%),　pentanes　(16.4%),　and　butanes　(13.4%),　which　is　consistent　with　the　knowledge　of　VOC　components　emitted　from　the　manufacturing　of　ethylene,　polyethylene,　and　polypropylene.　Then,　by　using　the　inverse-dispersion　calculation　method　(IDM),　we　determined　the　relationship　coefficient　gamma　between　source　emission　rate　and　ambient　concentration　for　each　receptor　of　each　test　based　on　an　assumed　source　emission　rate,　combined　gamma　with　the　actual　VOC　concentrations　measured　in　monitoring　tests,　and　estimated　the　average　VOCs　emission　of　666.0　tons/year　for　this　plant,　including　18.1　tons　for　ethane,　21.1　tons　for　propane,　61.6　tons　for　isobutane,　44.3　tons　for　n-butane,　79.3　tons　for　isopentane,　56.8　tons　for　n-pentane,　115.4　tons　for　ethylene,　102.5　tons　for　propylene,　92.7　tons　for　benzene,　and　74.1　tons　for　toluene.　Our　IDM　estimate　was　in　the　same　order　with　the　traditional　emission　factor　method　estimate　(916.4　tons　VOCs　per　year　for　this　plant),　and　we　believed　the　IDM　can　be　applied　to　effectively　estimate　the　VOCs　emissions　for　those　complicated　industrial　sources.