This article aims to understand the short-time severe rainfall events in the area of Sichuan and Chongqing more comprehensively, and provide references for improving operational forecast skills and numerical weather forecast skills. Based on a convection-scale ensemble forecast system, a short-time severe rainfall event that occurred in the area of Sichuan and Chongqing is selected, and then the ensemble sensitivity analyses of the average precipitation in the target region to the model initial values are carried out and the corresponding dynamic mechanisms are discussed. The results show that the distribution characteristics of sensitive areas correspond well with the synoptic systems that play a key role in the precipitation forecast of the target regions. The sensitive areas around the southwest vortex at 850 hPa and 700 hPa show positive and negative distribution characteristics, the left (right) side of the 500 hPa trough shows negative (positive) sensitive area, the high-level southwest jet area at 250 hPa (south side) shows positive (negative) sensitive area, and the corresponding areas corresponding with the front (back) of the front zone of the middle and low layers show positive (negative) sensitive area. These findings indicate that the stronger the northwest (southeast) wind in the negative (positive) sensitive area around the southwest vortex, the stronger the northwest (southeast) wind on the left (right) side of the trough, the stronger the southwest (northeast) wind in the upper jet stream zone (south), and the higher (lower) the pre-frontal (post-frontal) temperature is, the more favorable they are to the convergence upward movement in the southwest vortex, to the strengthening of the 500 hPa trough, to the strengthening of the 250 hPa divergence, to the increase of the temperature gradient in the frontal zone and to the strengthening of the frontal uplift, which finally result in positive impacts on the precipitation in the target regions.