A forest ecosystem consists of forest coenosis and environment, which are affected and interacted each other, with the function of energy transformation and storage. The forest ecosystem builds a perfect environment for rainfall interception and storage with its lush canopy, shrub layer and herb layer of undergrowth vegetation, forest floor litter, loose and deep soil layer. The forest ecosystem strongly affects rainfall redistribution and storage and thus plays its role as the unique function of water conservation. However, different forest ecosystems in different climate zones could exhibit big differences in characteristics of their water conservation functions due to different forest structure, topology, and soil properties. We selected four long-term forest ecosystem sites (Changbaishan, Beijing, Huitong, and Dinghushan sites) in our study. These study sites are located in the forest transect of eastern China across the semi-arid monsoon climate in the temperate zone, semi-humid warm temperate zone and subtropical monsoon climatic zone from north to south, with obvious thermal gradient and hydrologic gradient. We analyze stem flow, canopy interception of rainfall, rainfall through the forest, water holding capacity in forest litter layers and mineral soil layers, and overall forest water conservation capacity of nine forest ecosystem types across four study sites in the growing season during May to October. The results showed that: canopy interception varied significantly across different forest types from May to October. The retention rate were in order of Korean pine forest>firs>evergreen broadleaved forest>mixed coniferous and broad-leaved forest>monsoon evergreen broad-leaved forest>defoliate broad-leaved mixed forest>pinus massoniana forest>larix plantation forest>pinus tabulae-formis forest. The highest retention rate was Korean pine forest which was 2.2 times than the lowest, pinus tabulae-formis forest. The interception had significantly positive correlation to rainfall outside of the forest stands; canopy interception rate had significantly negative correlation to precipitation. We also found that the highest water-capacity of forest litter was deciduous broad-leaved forest in Beijing site, 6.0mm from May to October; the lowest water-capacity was monsoon evergreen broad-leaved forest in Dinghushan site, 1.0mm from May to October. The maximum water-capacity of the soil layer from 0 to 60cm depth was artificial fir in Huitong site, 247mm; the lowest was the larch in Beijing site, 45.5mm. Total water storage capacity of the forest ecosystem were in order of firs>Korean pine forest>evergreen broadleaved forest>mixed coniferous and broad-leaved forest>monsoon evergreen broad-leaved forest>defoliate broad-leaved mixed forest>pinus massoniana forest>larix plantation forest>pinus tabulae-formis forest. The total water storage capacity of different forest ecosystems fluctuated between 40-250mm during growing season. All of the subtropical forest ecosystems had higher values of water storage capacity, more than 100mm except the Pinus massoniana forest, 99.74mm; all forest ecosystems in semi-arid area of Beijing site had lower values of water storage capacity, less than 100mm. More than 90% of total water were stored in soil, followed by forest litter layer, about 8%, and then followed by forest canopy interception, about 2%. Our findings could promote the water conservation practice of forest ecosystems in eastern China.