Using the cyclostrophic wind equation of Rankine vortex, the vortex features of a tornado happened in Xixia county of Shandong Province are calculated. The maximum wind speed of a strong tornado, the maximum translatory velocity, the maximum tangential velocity, and the maximum atmospheric pressure drop are 62m·s^-1,12m·s^-1,50m·s^-1 and 27.5hPa, respectively. The assessment of tornado′s destructibility is given.