With the solar wind data observed by ACE／WIND spacecraft and the geomagnetic storm 〖WTB1X〗D〖WTB1〗st index data during 2004—2006,the linear correlation between magnetopause standard off distance 〖WTB1X〗R〖WTB1〗0 and 〖WTB1X〗D〖WTB1〗st index,in which the grade of geomagnetic storm is characterized,is investigated in terms of 200 different graded storms.It is a fact that the time series of 〖WTB1X〗D〖WTB1〗st index lag about 3 h behind the time series of the magnetopause standard off distance 〖WTB1X〗R〖WTB1〗0 calculated by Chao Model under the extreme solar wind.After the time lag corrected,the linear correlation between magnetopause standard off distance 〖WTB1X〗R〖WTB1〗0 and geomagnetic storm 〖WTB1X〗D〖WTB1〗st index is revealed.The results show that the average linear correlation coefficients are 077,074 and 047,respectively,corresponding to the super,the big and the middle storms.Under different graded storms,the charts of 〖WTB1X〗R0D〖WTB1〗st fitted by the least square method are shown.