Abstract: To investigate the effects of Castanopsis hystrix mixed with different tree species on the physical properties,chemical properties,and stoichiometric ratios of forest soil. 20-year-old Castanopsis hystrix mixed forests in Gaofeng Forest Farm were selected as the research objects. Differences in soil physical-chemical properties and stoichiometric ratios in the 0—30 cm soil layer were compared among three forest types:Castanopsis hystrix-Pinus massoniana mixed forest(MCP),Castanopsis hystrix-Acacia crassicarpa mixed forest(MCA) and pure Castanopsis hystrix forest(PCH). Based on 18 soil indicators,principal component analysis(PCA)was used to evaluate soil quality under different mixed forests. The results showed that:in terms of soil physical properties,Castanopsis hystrix mixed forests reduced soil bulk density and improved soil looseness. Specifically,MCP increased soil non-capillary waterholding capacity and non-capillary porosity,while MCA enhanced soil moisture content,maximum water-holding capacity,capillary water-holding capacity,field capacity,capillary porosity,and total porosity. Regarding soil chemical properties,Castanopsis hystrix mixed forests significantly increased soil pH. MCP improved the contents of soil organic carbon(SOC),total nitrogen(TN),ammonium nitrogen(NH₄⁺-N),and nitrate nitrogen(NO₃^--N),whereas MCA increased the contents of total phosphorus(TP),available phosphorus(AP),total potassium(TK) and available potassium(AK). For stoichiometric ratios,the carbon-to-phosphorus(C/P) ratio in the 0—10 cm soil layer of MCA was significantly higher than that in the 10—20 cm and 20—30 cm layers. PCA results indicated that the comprehensive soil quality scores of the three forest types followed the order:MCA > MCP > PCH. Overall,Castanopsis hystrix mixed forests effectively improved soil physical-chemical properties,enhanced soil structure,aeration,and water retention capacity and promoted soil nutrient accumulation. Among them,the mixture of Castanopsis hystrix and Acacia crassicarpa exhibited the best improvement effect on soil properties. This study provides a scientific reference for the selection of mixed tree species and cultivation of Castanopsis hystrix mixed forests.