Using the ARPS/ADAS cloud analysis system, the radar reflectivity factor is introduced into the initial field of the mesoscale numerical model. A severe hailstorm occurred in Beijing on 23 June 2008 is simulated. The study indicates that the hydrometeors and temperature field in the initiate field are improved significantly with the introduction of the radar reflectivity, and it makes the initial field closer to the actual atmosphere. Compared with the tests without cloud analysis, the simulations with cloud analysis are better in the formation position, intensity, and motion paths of hail clouds, especially for the simulation results within three hours. With the cloud analysis, precipitation and hail happen an hour earlier, and precipitation and the hail peak also occur earlier; the spin up time was reduced with the introduction of radar reflectivity information.