Abstract: Base on routine observation and Doppler weather radar data, a supercell storm in northwest of Hubei province is analyzed. The result shows that the dry and warm lid, strong vertical wind shear, upper divergence and low level convergence provided a favorable environmental condition for the supercell storm. Trumpet shaped topography, uplifted cold pool outflow and disturbance produced by lower level of warm air are the key factors for local thunderstorm' s enhancement. There are many supercell features in Doppler radar echo, such as hookecho, bounded weak echo region, vault, meso-cyclone, echo wall, etc. The results of 4D-VAR wind field retrieval show that the updraft at storm front and back and inflow in low level introduced a clear convergent rotational effect. When the dry cold updraft further advanced to the warm stream in low level, a strong inflow was formed. Then a strong divergent rotation at the upper level was produced. Middle level dry cold air entrainment makes the thunderstorm more organized and lasted longer, which is in favor of producing strong disastrous weather.