Applying the grid point field data of ECMWF,the diagnostic analyses to nine typhoonsfrom 1980 to 1992 which took a west turn while they moved north were made. The resultshows that when typhoons took west turns,there are warm advection,vapour flux convergence,stratification instability,aeroligical divergence and entire level cyclonic circlllation addition,and there is an entire level height descent center in the coverage of those additionarea,which result in typhoons to take a west turn while they move north.