Abstract: Quantitative analysis and evaluation of water-holding and carbon-fixing functions of vegetation communities have great significance to understand water conservation and carbon sequestration of desert vegetation communities．Four typical plant communities (Larix principis-rupprechtii, Betula platyphylla, Hippophae rhamnoides and grassland) in the Diediegou small watershed of semi-arid area in Liupan mountains, Ningxia, China were studied in this work．Field measurement and quantitative comparison of water-holding and carbon-fixing functions of litter layer and soil layer were conducted．Water-holding capacity of litter layer and soil layer of plant communities was analyzed by entropy weight method (EWM)．The relationship between soil organic carbon content and holding water capacity was analyzed by path analysis．Maximum water holding capacity of litter layer of these 4 plant communities was found to range from 3.03 to 20.55 t·hm⁻², effective storage capacity range from 2.13 to 14.58 t·hm⁻²; the largest was found with Betula platyphylla, being 1.4, 3.0 and 6.8 times of Larix principis-rupprechtii, Hippophae rhamnoides and grassland, respectively．In the 0-100 cm soil layer of these plant communities, maximum water holding capacity was found to range from 515.0 to 563.9 mm, capillary water holding capacity range from 377.8 to 423.1 mm, with Larix principis-rupprechtii showing the best soil water retention．Mean organic carbon content of 0-100 cm soil layer of these 4 plant communities ranged from 23.89 to 26.43 g·kg⁻¹, the highest was found with Larix principis-rupprechtii, the lowest Betula platyphylla．Soil organic carbon content was found significantly positively correlated with soil water retention properties (total porosity, capillary porosity, maximum water holding capacity, capillary water holding capacity)．The comprehensive evaluation results of water-holding and carbon-fixing functions of litter layer and soil layer of Larix principis-rupprechtii were the highest (0.330), followed by Betula platyphylla (0.303), grassland (0.218) and Hippophae rhamnoides (0.148)．The above data suggest that water-holding and carbon-fixing functions of litter layer and soil layer of Larix principis-rupprechtii are better than other plant communities, and should be given priority when site conditions are better．This study will facilitate restoration and multi-functional optimization management of forest vegetation in semi-arid Liupanshan area．