Abstract: Theunusual path andtheasymmetric structureof typhoon Utor in its anomaly movement and thevanationofciculatiom and steering flowwere studied.The reasons of its suddenly changed path and the forecast eror werefound.The results showed that,the sudden change of ciculation was the most important reason of typhoon Utorscomplicated path in thefinal phase of its life.After typhoon Utor moved into the South ChinaSea,a strong and sta-ble squareshaped subtopical high was located on the west Pacific,and then weakened and moved northward fol-lowing a temporary westwand strengthening,and the continental cold high moved southward at last.typhoon Utorwas dominated in turn by southeasterly,thensoutherly,at last northeasterly steering flow,corresponding to the var-iation ofcirculation.The path of typhoon Utor was closely related to the direction and strength of the geostrophicstering flow on 500 hPa.The change of steering flow happened before the change of path.When thedirection ofsteering flow changed,thedirection of path changed.When thesteeringflow weakened,the velocity of typhoonUtor reduced.Coresponding to 3 diferent stages of changing path,typhoon Utor's asymmetric structure wentthrough 3 stages.The NE—SW stage(the stream was intensive at the northeast side and sparse at the southwestside),then the SE—NW stage,at last thestage that NW—SE was much significant,coexisting with NE—SW.The asymmetrie structure also impacted on the path.The path prediction madeby numericalmodels should be cor-rected acconding to the changes ofthe subtropical high and typhoon's asymmetry structure.