Abstract: A squall line event in northern Jiangsu in midsummer is simulated and analyzed by adopting regional WRF model with triple nesting, and the conceptual model diagram in the radial section of squall line is given. The main results are as follows. The simulated and actual squall lines are very similar, they both have the same nature and characteristics. Thus, it is feasible to determine the location and intensity of squall lines using the range and intensity of the simulated linear strong precipitation zone. There are areas of strong convergence, strong ascending motion and high value of pseudo equivalent temperature in the squall line during its mature stage. These three all have the columnar structure and vertical extent. There is an inflow of high value of pseudo equivalent potential temperature in the lower layer in front of the squall line (the moving direction of squall line), which brings a large amount of water vapor and energy to the squall line. There is a shallow inflow in the lower layer behind. The direction of surface wind changes sharply when the squall line passes through. The potential temperature is almost constant and appears as a neutral stratification in the middle layer of squall line, which is related to the release of convective condensation latent heat. The squall line event can be regarded as pseudo adiabatic process and has the unbalanced property of gravity wave. Thus, there are multi-scale interactions in its generation and evolution.