In recent years，the urbanization process of Nanning has accelerated significantly，but at the same time，heavy precipitation has also shown a trend of frequent occurrence and increased extremity. To this end，this study used the Weather Research and Forecasting system coupled with Urban Canopy Model（WRF-UCM），the ERA5 reanalysis data，and sensitivity test to simulate the heavy precipitation process of a low vortex type in Nanning in May 2022. Results show that：（1）After updating the land use information and coupling the urban canopy model，the simulation results of 6-hour cumulative rainfall are consistent with the observed results in the spatiotemporal distribution，and more accurately reflect the evolution of precipitation intensity in the main urban area； （2）Under the background of hilly basin topography，the circumfluence effect and the intensification of the heat island effect，both resulting from changes in surface characteristics driven by Nanning's urban land expansion， are the main factors contributing to precipitation changes，which causes the occurrence time of heavy precipitation to increase by 1~2 hours and the precipitation increase by 10%~30% from the main urban area to the down‐ wind area 20km，and the precipitation in the southern suburbs and upwind area decreases by about 15%；（3）In the development stage of precipitation process，the decrease of latent heat flux and convective effective potential energy（CAPE）caused by urban land expansion will inhibit the development of deep convective precipitation， but the urban heat island effect caused by the increase of sensible heat and surface soil heat flux in urban areas， as well as the enhancement of urban surface friction and circumfluence on the convergence and uplift of near-sur‐ face airflow，promote the increase of cloud and rainfall content and the new development of convective clouds in the front of the low vortex，resulting in the early occurrence of heavy precipitation in urban areas and downwind areas. In the later stage of the precipitation process，the enhanced airflow caused by the proximity of the center of the low vortex makes the effect of circumfluence more obvious，and the re-evaporation of surface water vapor caused by the enhancement of precipitation and the increase of latent heat of condensation at 925~700 hPa have a positive feedback effect on the enhancement of the low vortex，which jointly drives the development of warm cloud precipitation process and improves the precipitation efficiency，and the development of local circulation in the city promotes the mutual transformation of ice particles and rainwater in convective clouds，resulting in the maintenance of convective cloud intensity. As a result，the duration of heavy precipitation is prolonged，resulting in an increase in accumulated rainfall.