With radar and automatic meteorological observing station data, a tornado course was studied. System structure during the development of tornado and the change of circumstance characters were analyzed in detail, and the inducing causes of the tornado course also were discussed dynamically in this paper. The results indicate that the tornado forms in highly converging area of cyclonic vorticity. Also dry and cold air invading from middle troposphere result in convective instability structure of cold advection at the upper level and the warm advection at the lower level. When strong wind band moved toward vorticity converging area, mesocyclone series is induced on the wind band. Strengthening of convective instability led to strong development of vertical convection in the mesocyclone, which results in the occurrence of tornado. And further dynamical studies show that the inclination term of vorticity equation plays an important role in the variation of mesoscale disturbance vorticity and it is one of the important causes brought about tornado when there is stronger vertical wind shear in wind field.