Abstract: [Objective] To investigate variations in water conservation capacity among Chinese fir plantations of different ages in southern low-mountain hilly regions, providing a basis for understanding the water conservation capabilities of Chinese fir plantations and their scientific management. [Methods] Five cypress plantations with different growth ages (3, 4, 7, 8, and 11 years) were selected based on planting conditions. Field surveys combined with laboratory experiments were conducted. Single-factor analysis of variance was applied to study the litter layer (accumulation, water-holding capacity, retention capacity, and water retention process) and the soil layer (bulk density, porosity, saturated hydraulic conductivity, and retention capacity). The overall water conservation capacity of each stand was comprehensively evaluated by cumulatively calculating the water conservation amounts from both layers. [Results] (1) Water conservation capacity of the litter layer across the five stands ranged from 8.51 to 17.10 t/hm2, with the following order of magnitude: 11year > 4year > 3year > 8year > 7year. (2) Water conservation capacity of the soil layer across the five stands ranged from 352.90 t/hm2 to 504.58 t/hm2, with the order of magnitude being 8 years > 7 years > 11 years > 4 years > 3 years. (3) The total water conservation capacity of the litter layer and soil layer ranged from 362.96 t/hm2 to 513.45 t/hm2, with the order of magnitude being 8 years > 7 years > 11 years > 4 years > 3 years. [Conclusions] (1) Water conservation capacity in the litter layer, soil layer, and forest land of Chinese fir stands increases nonlinearly with growing age. (2) Litter layer water conservation capacity is primarily influenced by litter accumulation and decomposition rate, while soil layer capacity is mainly affected by tree root growth and soil nutrients. (3) The soil layer accounts for over 95% of total effective water storage, making forest soil the primary water-retaining component in the stand. (4) Recommendations: For stands aged 3-4 years, focus primarily on the soil layer by improving soil physical structure to enhance permeability. For stands aged 8-11 years, which may enter a decline phase, enhance water retention by increasing soil nutrients, managing litter accumulation and decomposition appropriately, and potentially implementing mixed stands of cypress and broadleaf trees. These findings provide theoretical references for the sustainable management of cypress plantations. Keywords: Cedar forests; Water conservation; Litter layer; Soil layer