Using the highresolution mesoscale model WRF, a strong squall line process on April 17, 2007 in South China was simulated.The numerical simulation results were used to make the diagnostic analysis on the strong squall line process, a nd to explore its trigger and maintenance mechanism. The results show that low l evel mesoscale convergence line and shear line are one of the main trigger syste ms of this squall line process and one of the important maintenance mechanisms. And also the dry invasion and con vective instability, and convergence and divergence from bottom to top play an i mportant role in the development and maintenance of the squall line.In addition, mesoβ scale structure characteristics of the strong squall line process are successfully simulated, indicating that the WRF model has a certain simulation capability of strong convective weather systems.