Based on the single-Doppler weather radar observations and 255m meteorological tower data, the thunderstrom occured from 20:00 to 21:40, June 22, 2004 in Tianjin area is analyzed. It is proved that thunderstrom can be caused by convective system with bow echo, and strong wind can bring on outflow boundary, and further proved the top and the middle of the bow echo can generate severe strom. In addition, the airflow structure of thunderstrom is discussed also.