For the heavy rainstorm event in Zhengzhou on 20 July 2021, the influence of water vapor and upper-low-level jet in this extremely heavy precipitation process is analyzed by numerical experiments using the CMA-MESO regional model. The results show that the rainstorm process can be successfully simulated by mesoscale model. The main water vapor sources during the rainstorm are the water vapor from the western Pacific and Indian Ocean carried by the southeast jet on the north side of Typhoon In-fa and the water vapor from the South China Sea carried by the southeast jet on the north side of Typhoon Cempaka. Precipitation and water vapor transport are very sensitive to water vapor content, which shows that the slight change of water vapor content can weaken the intensity of airflow convergence zone over Zhengzhou, reduce the accumulation of water vapor, narrow the precipitation area to the north of Henan, and greatly weaken the precipitation intensity. The airflow convergence zone corresponding to the low-level jet is the main mechanism causing the strong vertical ascending motion center over Zhengzhou. The weakening of the low-level jet makes the convergence of water vapor decrease, which leads to the decrease of precipitation and the location of precipitation center to the southwest. The influence of upper-level jet on precipitation is less than that of low-level jet.