[Objective] In this study, we aimed to explore the mixed plantation with the optimal water conservation capacity of Mytilaria laosensis and Castanopsis hystrix, which would be benefited for construction and management of water conservation forest in Xijiang river valley located in Guangdong province. [Method] The nine mixed plantation patterns within three mixed proportion (i.e., 1:3, 2:2 and 3:1) and three mixed modes (i.e., interplant mixing, mixture in strip and row, block mixing) of Mytilaria laosensis and Castanopsis hystrix were selected, and the pure plantations of Mytilaria laosensis and Castanopsis hystrix were controls. The differences of water conservation capacity in litter and soil varied the eleven mixed plantations were evaluated, and then the mixed plantation with the optimal water conservation capacity was screened out using an entropy weight TOPSIS (Technique for Order Preference by Similarity to an Ideal Solution) model. [Result] (1) The biomass, natural water storage, effective water interception amount and maximum water interception amount in litter layer were 1.17~4.21, 0.38~2.29, 5.15~10.58 and 6.40~13.37 t·hm-2, respectively. These indexes were positively and significantly correlated with the number percentages of Mytilaria laosensis in the plantations (P＜0.05). Compared to the interplant mixing and block mixing of the plantations, the mixture in strip and row of the plantations had higher biomass and effective water interception amount in litter layer. (2) The natural moisture storage, capillary water storage, non- capillary water storage and saturated water storage in soil at the depth of 0—30 cm were 756.14~1007.21, 1130.73~1388.40, 117.96~422.63 and 1444.70~1590.66 t·hm-2, respectively. The capillary water storage and non-capillary water storage were significantly different among the different plantations, and were significantly correlated with the number percentages of Mytilaria laosensis in the plantations (P＜0.05). (3) The water conservation capacity in the plantations was evaluated using an entropy weight TOPSIS model, indicating that the mixed plantation of Mytilaria laosensis and Castanopsis hystrix with a ratio of 3:1 and mixture in strip and row had the optimal water conservation capacity. The water conservation capacity of other plantations in the following order: the pure plantation of Mytilaria laosensis, the other mixed plantation patterns and the pure plantation of Castanopsis hystrix. [Conclusion] The water conservation capacity of mixed plantation of Mytilaria laosensis and Castanopsis hystrix to some extent better than each pure plantation in the young stand stage, which would be affected by the mixed proportion and modes.