A diagnostic analysis is made of a hail event happened in Ninglang in the northwestern Yunnan Province. The results indicate that the main objective conditions of this hail process include abundant moisture, instable stratification and strong vertical ascending motion. Before the process, the water vapor and dynamical forcing conditions were not favorable, except the unstable conditions. By analyzing the numerical prediction products before the hail process, the forecasting of major impact systems, water vapor, uplift motion, and instability conditions were conducted. The forecasting and warning of severe hail events can be well realized by analyzing the major influence systems, physical diagnostic products, including numerical forecast products, in combination with satellite images and radar echo data.