In　order　to　compute　left-turn　delay　under　complex　traffic　flow　more　scientific,　the　regulation　of　vehicles　arrival　and　departure　is　analyzed.　This　paper　proposes　a　new　approach　to　calculating　left-turn　delay　at　signalized　intersection　based　on　the　incremental　queue　accumulation　(IQA)　method.　This　method　uses　the　cumulative　area　of　the　queue　of　irregular　polygon　as　a　uniform　delay　values.　The　method　breaks　Webster＇s　delay　model　conditions　and　description　the　actual　traffic　conditions　better.　The　new　method　is　tested　using　the　field　data　colled　at　several　signalized　intersections　in　the　city　of　Fuzhou.　The　IQA　method　is　more　realistic　than　the　Webster＇s　delay　model,　especially　the　permitted　left-turn　operation　at　signalized　intersection.