Water conservation is one of the important ecological services restricting regional sustainable development, which is of great significance to regional industrial and agricultural production, life and ecological protection and construction. Therefore, the research on ecosystem water conservation has become an important field of ecological service research. It is of great significance for the protection and management of ecosystem water conservation for China to explore the spatio-temporal variation of ecosystem water conservation. To reveal the spatio-temporal pattern and evolution of ecosystem water conservation in China, the water balance equation was used to estimating ecosystem water conservation in China from 1990 to 2018. Based on the Matlab platform, the spatio-temporal patterns and change trends of China's ecosystem water conservation were revealed on national, regional and grid scales using spatial statistics and trend analysis method. The main results were as follows:(1) The spatial and temporal heterogeneity of water conservation in the Chinese ecosystem was significant, which decreased from south to north, and from east to west. There were significant differences in water conservation capacity among different vegetation types, which was highest in evergreen broadleaved forests and lowest in grasslands. (2) The ecosystem water conservation decreased with altitude, however, its variation characteristics were different in different slope gradients. The ecosystem water conservation increased with the increase of slope in flat slope area, while in gentle slope to steep slope area, it decreased with the increase of slope with little fluctuation. (3) The amount of annually average ecosystem water conservation in China was about 1.54×10¹² m³/a, which was dominated by the tropical and subtropical monsoon zonal with 1.20×10¹² m³/a, accounting for about 77.9% of the total. The ecosystem water conservation in China decreased significantly at national scales from 1990 to 2018. Only the temperate continental climate zone had a significant decrease in ecosystem water conservation, and no significant change in the others at regional scales during the study period. (4) The ecosystem water conservation of most grids did not change significantly from 1990 to 2018 on grid scales, accounting for about 84.01% of the total grids. The grids with significant changes in ecosystem water conservation were mainly extreme decrease and significant decrease, accounting for 7.61% and 5.30% of the total grids, respectively, which were mainly distributed in southeastern Tibet, western Sichuan, northern, central and western Yunnan, northeastern Hebei, Hunshandake Sandy Land, eastern Tianshan Mountain and Taiwan province, where were the key areas of water conservation, protection and construction in China. The total of grids with extreme and significant increase in water conservation totally accounted for 2.36% of the total grids, which mainly scattered in central Qinghai, Qinling Mountains, Northeast Plain and the northern Greater Khingan Mountains. Based on the distributions of significant changs in the ecosystem water conservation in China on grid scales from 1990 to 2018, the leading driving factors for ecosystem water conservation changed significantly could be revealed by combining the spatial data of China's ecological protection and construction, climate variations, landuse change and urbanization construction. Therefore, the study can provide data support for the conservation and regulation of water resources in China's ecosystem.