In order to compare and analyze the impacts of stand density on hydrological and ecological functions of litter layer, the Robinia pseucdoacacia plantations with 6 different densities (475, 900, 1 200, 1 575, 1 825 and 2 350 trees/hm²) in Loess region of Western Shanxi Province were chosen as the object. By the methods of field survey and laboratory experiment, the hydrological characteristics of litter layer, such as the litter total storage capacity, the maximum water holding capacity and modified interception capacity and their relationships with soaking time, were studied, aimed to propose the reasonable density of the Robinia pseucdoacacia management in this area and provide scientific basis for giving full play to soil and water conservation functions as well as achieving function-oriented vegetation regulation and optimal allocation. The results showed that:(1) The litter total thickness of Robinia pseucdoacacia plantations with 6 densities ranged from 28.67 mm to 54.33 mm in the studied area. The total volume was about 2.98~10.65 t/hm², and in a certain stand density, the litter total storage capacity increased first and then decreased with the increase of densities, showing an order of 1 575 trees/hm² > 1 825 trees/hm² > 1 200 trees/hm² > 900 trees/hm² > 2 350 trees/hm² > 475 trees/hm². (2) The maximum water holding rates varied from 295.35% to 427.84% with no obvious regularity. The maximum water holding capacity was 11.16~37.01 t/hm² and had significant differences among some plantations with different densities, which achieved the best (37.01 t/hm²) at 1 575 trees/hm². The water holding capacity in half-decomposed litter layers was higher than that in un-decomposed litter layers, but different stand densities had little effects on water absorption rates. (3)The modified interception capacity was about 7.22~23.64 t/hm² in different stands and the maximum was found in 1 575 trees/hm², reaching 23.64 t/hm². (4) Water holding capacity of litter had a logarithmic correlation with immersion time (Q=aln t+b, R²>0.95), and water absorption rates showed a power function with soaking time (V=ktⁿ, R²>0.99). In summary, within the scope of this study, the litter layer showed better hydrological and ecological function under plantation with around 1 575 trees/hm². When the density was lower than 1 200 trees/hm², it tended to drop sharply. From the perspective of litter hydrological function, it is recommended to maintain the rational stand density range of 1 200~1 800 trees/hm² in future Robinia pseucdoacacia plantation management of this area.