In order to investigate the water conservation function of litter and soil in typical forest lands and provide the basis for tree species selection and stand improvement by functional orientation in Gully region of Loess Plateau, the Robinia pseudoacacia L., Pinus tabulaeformis, and mingled forest were chosen as subjects in this article at Caijiachuan watershed in Ji County of Shanxi province in 2017. The water conservation function was studied by quantitative research with Immersion method and cutting-ring method applied to litter and soil in typical forest lands. The results showed: (1) The total litter storage capacity of the three kinds of forest lands ranged from 105.49 to 148.38 t/hm2, and the storage capacity of semi-decomposed litter was higher than that of undecomposed litter. The total litter thickness of mingle forest composed with R. pseudoacacia L. and P. tabulaeformis was the highest as 3.8 cm, the second was R. pseudoacacia L. forest as 3.6 cm, while the Pinus tabulaeformis was the lowest, 3.4 cm. (2) By analyzing the rules of maximum water-holding capacity and maximum water-holding rate, the mingle forest was the highest and the R. pseudoacacia L. and P. tabulaeformis was the second and the third respectively, the values were 117.99 t/hm2 and 387.12%, 106.19 t/hm2 and 324.31%, 82.86 t/hm2 and 305.76%, respectively. (3) The effect interception amount and the effect interception rate of litter in broad-leaf forest was more than that in coniferous forest. The effect interception amount ranged from 83.66 to 195.72 t/hm2, and the effect interception rate ranged from 121.75% to 292.21%. The relationship between the water-holding capacity and the immersion time fitted Logarithmic Function, and the relationship between the water-absorption rate and the immersion time fitted Exponential Function. (4) The average of soil bulk density of three kinds of forest land ranged from 0.99 to 1.01 g/cm3, and the total soil porosity varied from 49.39%～50.09%, and the soil water-holding capacity varied from 32.99～81.73 t/hm2. By analyzing soil infiltration rate and infiltration time, we found that there is a power function relation between them. Considering the water-holding abilities of the litter and soil of three kinds of forest lands, the water conservation abilities of the mingle forest was the highest, while that of the P. tabulaeformis was the lowest. Therefore, the existing R. pseudoacacia L. and P. tabulaeformis forest should aim at mingle forest in the stand improvement.