Abstract:By using Jinan CINRAD/SA Doppler radar products, the weather proces s of squall line on July 5, 2006, evolution of echo and flow structure were anal yzed, the relations between the outflow boundary, sinking air currents and stron g wind were discussed，and the portfolio reflectivity factor, the vertical liqui d water content, the mesocyclone product characteristics were analyzed. The resu lts showed that two maxima of wind speed occurred during the squall line passing, one appeared in an outflow boundary impact sessions, another in strong echo si nking airstream affected periods. As the transverse trough moves southward, the inflow continuously added to the rear of squall line, the warm and wet air flow climbed along the rear of inflow, which constantly created new cells and maintai ned the development of storm. In the vertical flow structure, the warm air for t he front side was tilted upwards, and the main part tilled backwards. In the rea r there was the cold air injected and the downward flow formed. The sinking air near the ground diverged, together with the lateral inflow formed the lower gust front, which was the major factor causing the ground destruction. In the horizo ntal flow structure there was an upward motion of convergence at low level and a cyclone rotational flow at the middle level. At high level there was a diverge nce flow. In the dissipating period of squall line, MARC appeared at middle level , which brought strong winds and hail weather. The wind disaster with hail produ ced in the period when the squall line was the strongest and began to weaken. Wh en the echo intensity≥50dBz and vertical liquid water content ≥35 kg·m- 2, the meso cyclone is favorable for generating of hail and strong wind. The emerg ence of outflow border reflected that the strong sinking flow in the rear of stro ng echo is a precursor of the disastrous wind.