To study the growth status and water conservation capacity of water conservation forests in the mountainous areas of northern Hebei in the upper reaches of the Miyun Reservoir, four mixed forests, Pinus tabulaeformis×Larix (woodland I), Pinus tabulaeformis×Apricot (woodland Ⅱ), Pinus tabulaeformis×Quercus mongolica (woodland Ⅲ), and Platycladus orientalis×Apricot (woodland IV), were studied. Through the analysis of the characteristics of the litter layer and soil layer under the forests, the water-holding capacity of the litter and soil and the water conservation capacity of the forest land were analysed and compared. The results showed that the existing litter amount was in the order of woodland Ⅱ > woodland IV > woodland I > woodland Ⅲ. The litter layer of woodland Ⅱ had the largest effective water-holding capacity, which was 81.30 t/hm², and that of woodland I had the lowest water-holding capacity. Soil total porosity, capillary porosity, and non-capillary porosity were the highest in woodland IV (56.02%, 50.26%, and 5.76%, respectively). The soil layer of woodland IV had the most effective water-holding capacity, which was 1507.90 t/hm², and that of woodland Ⅲ had the lowest water-holding capacity. Upon determining the water-holding capacities of the litter and soil layers of the four woodlands, the water conservation capacity was determined to be the strongest in woodland IV (P. orientalis×Apricot), 157.43 mm, and weakest in woodland Ⅲ (P. tabulaeformis×Q. mongolica).