Scholars often overlook the complexity of the terrain, an important factor influencing the equalization of regions’ basic public services. This study utilizes data from 278 prefecture-level cities in China from 2011 to 2021. It employs the ASTER GDEM 30M resolution digital elevation data to identify and extract terrain complexity characterized by slope, elevation, and topographic variation. It empirically examines the terrain complexity’s impact on the equalization of regions’ basic public services and its underlying mechanisms. The results reveal that as terrain complexity increases, the equalization level of regions’ basic public services decreases. The mechanism analysis infers that terrain complexity aggravates the degree of fiscal decentralization, resulting in a wider disparity of basic public services among regions. Additionally, the exploratory analysis divulges that the expansion of communication networks augments the complex terrain’s impact on widening regional disparities in basic public services.