[Objective] The water conservation ability of the litter and soil layers of Alnus formosana mixed plantations was studied in order to provide a theoretical basis for the rational management and utilization of A. formosana in the Guangxi Zhuang Autonomous Region.[Methods] The entropy weight method was used to comprehensively evaluate the hydrological effect related factors. The mixed modes included A. formosana and Pinus massoniana, A. formosana and Eucalyptus grandis×urophylla, A. formosana and Castanopsis hystrix, and an A. formosana pure plantation as the control.[Results] ① The maximum water holding capacities of litter were largest in the mixed A. formosana and C. hystrix plantation with a 2:1 ratio and least in the mixed A. formosana and P. massoniana plantation with a 1:1 ratio. The effective retention rate of litter in the mixed A. formosana and C. hystrix plantation (with a 1:2 ratio) was the highest, the effective retention amount in the mixed A. formosana and C. hystrix plantation (with a 2:1 ratio) was the highest, whilst the effective retention rate and amount in the mixed A. formosana and E. grandis×urophylla plantation (2:1) were the lowest. ② The soil bulk density in the mixed plantations was significantly lower than that in the pure forest, however, the total porosity, capillary porosity, natural water content, maximum water holding capacity, and capillary water holding capacity of the soil were all higher in the mixed plantations. ③ The entropy weight method was used to calculate the weight value. The maximum water holding capacity of the litter was the largest, and the soil capillary porosity was the smallest. The comprehensive evaluation of the water conservation ability was ranked as follows:A. formosana and E. grandis×urophylla (1:2) > A. formosana and C. hystrix (2:1) > A. formosana and P. massoniana (1:2) > A. formosana and C. hystrix (1:1) > A. formosana and E. grandis×urophylla (1:1) > A. formosana and P. massoniana (2:1) > A. formosana and C. hystrix (1:2) > A. formosana and E. grandis×urophylla (2:1) > A. formosana and P. massoniana (1:1) > CK.[Conclusion] The water conservation ability of the mixed plantations of A. formosana was better than that of the pure plantation.