In order to explore the impact of underlying surface changes on precipitation in high-density urban areas, the distribution information of impervious surface in the main urban area of Zhengzhou City from 1990 to 2019 was estimated based on the remote sensing technology, and the expansion characteristics were analyzed. A regression model was used to explore the correlation between the proportion of impervious surface and the change of precipitation characteristics, and the threshold value of impervious surface proportion significantly affecting precipitation in the main urban area was identified. The effects of impervious surface expansion on precipitation in the main urban area were revealed from multiple angles with the method of comparison between urban and suburban areas. The results show that the impervious surface exhibited a significant expansion trend, like spreading a pie with a single core, in the main urban area of Zhengzhou City. The proportion of impervious surface had a quadratic polynomial function relationship with the ratio of precipitation intensity, and its threshold significantly affecting precipitation in the main urban area was 30%. The impervious surface expansion resulted in a significant rain island effect in the main urban area, and the maximum precipitation enhancement coefficient was 1.39. The probability of rainstorm in the main urban area was 53% higher than that in the suburbs, and the precipitation concentration period was about 8d later than that in the suburbs. The contribution rate of impervious surface expansion to precipitation change in the main flood season was 44.39%. Impervious water surface, with characteristics of high heat storage capacity and low permeability, has a significant impact on surface thermal and dynamic conditions, and has become one of the main factors of urbanization affecting precipitation.