Based on the velocity and intensity field data from CINRAD WSR 98D weather radar, an analysis was made of the squall lines on 5 April 2002 in conjunction with the radiosonde data and 500 hPa and surface weather data at the same day. Results indicate that there were obvious characteristics in the surface and upper level weather patterns and in stratification stability, as well as in Doppler radar echoes during the formation and development periods of the squall lines.