In this study, we analyze the evolution of the dynamical field before the occurrence of convection by using the dynamical parameter profiles below 4 km inverted from the wind profile radar mesoscale network from April to September during 2023-2024. The results show that before the convection triggering, the dynamical field is characterized by a vertical upward motion configuration with low-level convergence and high-level divergence. There exists the presence of positive time-lag correlations between area averaged rainfall and convergence in the lower to mid-troposphere. During the 30 min before precipitation, horizontal divergence is less than -5×10-5 s-1, with the convergence thickness below 1 km deepening, which means that the continuously enhanced convergence and upward motion favors the occurrence of convection. The horizontal convergence intensity sustained to be greater than 50×10-5 s-1 in the 30 min prior to precipitation is used as an indicator for the early signal of convection triggering. Among 763 precipitation events, the accuracy rate of effective identification of precipitation events is 72.3%. These findings can provide an important reference for quantitatively analyzing the early warning of severe convection in Beijing-Tianjin-Hebei Region.