The WRF mesoscale model is used to simulate the process of a strong squall line occurring in South China from March 30 to 31, 2014. The squall line process is affected by the high-altitude trough and the low-vortex shear line, the water vapor conditions are sufficient, and the low-level vertical wind shear is strong. Results show:in the development stage, the rear inflow gap begins to appear, and the squall line gradually becomes an arched structure; at the maturity stage, the inflow from the rear of the squall line gradually sinks to the ground and extends to the front of the convective zone. The cold pool is completely moved into the residual cold zone and strengthened. With the Jiulianshan Mountain downhill process, the squall line is strengthened. The Rear Inflow Jets(RIJ) are very important for the development and maintenance of this squall line process. The rear inflow jets are formed by the ambient wind and the middle layer negative pressure disturbance action, and then rapidly developed and enhanced under the influence of the middle and lower layer vortex pairs on the back side of the convection zone. In the development stage, the north wind field of the anticyclonic vortex promotes the formation and development of the rear inflow jets; at the maturity stage, the south side wind field of the cyclonic vortex rapidly increases the rear inflow jets. The cyclonic vortex is mainly increased due to effect of the stretching term, while the anticyclonic vortex is mainly increased due to effect of the tilting term. The vertical vorticity of the vortex pairs is mainly caused by the upward tilt of the low level horizontal vorticity which is caused by the baroclinic term.