Abstract: As one of the important ecosystem service functions, water conservation function is of great significance to the ecosystem and water safety in the Zhangjiakou and Chengde districts. Based on the integrated valuation of ecosystem services and tradeoffs (InVEST) model, this study quantitatively evaluates the water conservation function and analyses its driving factors of the Zhang-Cheng district from 2001 to 2020 using high-quality remote sensing data and other reanalysis products, in order to improve the problems of insufficient consideration of topography and soil permeability, as well as the inadequate analyses of data spatial heterogeneity in previous studies. The results show that the spatial distribution of the water conservation function in the Zhang-Cheng district from 2001 to 2020 was characterized by high values in the Baxia areas and low values in the Bashang areas. Despite some differences, the spatial distribution of the water conservation function in each year had some similarities to some extent. In terms of the trend, the water conservation depth in these 20 years showed a fluctuating downward trend with an average rate of −0.08 mm/a. Combined with the Sen+Mann-Kendall analysis, the trend of the water conservation function in this area was mainly classified as "No trend", "Slight increase" and "Slight decrease", accounting for nearly 98% of the total area. The results of correlation analysis show that precipitation had a strongly significantly positive correlation with water conservation function, temperature had a significantly negative correlation with water conservation function in some areas, and the correlation between vegetation and water conservation function was complex. In the Zhang-Cheng district in 2020, the woodland had the strongest water conservation function, and the water conservation depth reached 28.64 mm. On the other hand, the grassland water conservation function had the greatest contribution in the total amount, and the water conservation reached 1.12×10⁹ m³. During these 20 years, the water conservation of the farmland had the most obvious decrease, with a rate of −6.49×10⁶ m³/a. The spatio-temporal change characteristics of water conservation function in the Zhang-Cheng district in these 20 years were mainly controlled by precipitation and vegetated land use. This study provides an important decision-making basis for ecological construction and water resources management in the Zhangcheng district.