An extreme heavy rainfall event in Henan Province (HnHRE) of central China in July 2021, which is jointly affected by the western Pacific subtropical high (WPSH) and Typhoon In-Fa (2021), is comprehensively studied through five experiments conducted using the Weather Research and Forecasting Model (WRF). The patterns of the WPSH, In-Fa, and precipitation are well reproduced in the control experiment. In SH150 and SH050 (TC150 and TC050), the magnitudes of PV anomaly associated with the WPSH (In-Fa) is increased and decreased by 50% in the initial condition, respectively, based on the piecewise potential vorticity inversion (PPVI). The analysis shows that the 54-h rainfall accumulations in TC150 and TC050 are reduced by 37.2% and 35.1%, respectively, more than 28.1% in SH150 and 24.1% in SH050, indicating that Typhoon In-Fa plays a more critical role in the rainfall amplification than the WPSH. The WPSH and In-Fa majorly control the meridional and zonal moisture transports, respectively. The diagnosis of moist ageostrophic ω turns out that diabatic heating is closely related to the vertical motion during the HnHRE. Besides, the heavy rainfall region is also closely attributed to the distributions of other dynamical and thermal factors.