Comparative analysis of two rainstorm processes was conducted using methods of synoptic diagnosis and numerical experiment with the NCEP 1°×1° reanalysis, and Ningxia regional automatic station observation, and FY-2E satellite data. These rainstorms occurred on the east side of the Helan Mountain from July 18 to 19, 2018 and June 4 to 5, 2017, which were all accompanied by low-level jet. (1) The “7·18” process is a short-term rainstorm, which is produced by the interaction of a high-altitude trough and southerly low-level jet under the circulation background of “high in the east and low in the west” at 500hPa, while the “6·04” process is a large-scale continuous precipitation process formed under the influence of the stable large-scale trough and the southeast low-level jet. (2) The difference in the impact of the low-level jet on the two rainstorms may be due to the different distribution patterns of the low-level jet. The low-level southerly jet before the “7·18” heavy rain mainly played the role of transporting water vapor. When the low-level jet strengthened and interacted with the Helan Mountains, the rainstorm was induced, and the southerly low-level jet was deflected into the southwest low-level jet. The low-level jet and the rainstorm process promoted each other to strengthen the precipitation. The northern part of Ningxia is always located on the southeast side of the mesoscale vortex and the left side of the southwest low-level jet during the “6·04” rainstorm. It is a favorable dynamic condition for the rainstorm. (3) Results of the numerical sensitivity experiment indicate that the precipitation intensity is weakened in the two rainstorms after decreasing intensity of the low-level jet; the reduced areas are located near the Helan Mountain and the central area of Ningxia plain, respectively. Among them, the south wind component of the low-level jet has an important impact on the precipitation intensity. (4) Results of diagnostic analyses show that the impacts of the low-level jet strengthen the dynamic effects of vertical movement at the windward slope for the “7·18” process, and the impact on the “6·04” process is mainly reflected in the dynamic convergence and uplift on the left side of the low-level jet. The influence of water vapor transport in the “7·18” process is greater than that in the “6·04” case.