【Objective】 Chestnut (Castanea mollissima) is a woody grain species widely cultivated in China. Given the quick-acting effect of inorganic fertilizer and the persistence of organic fertilizer, the combined application of organic-inorganic fertilizer can play an important role in fertilizing the soil and promoting root growth. Effects of organic and inorganic fertilizer application on soil fertility and root functional traits in a chestnut orchard were examined to provide a theoretical basis for scientific, reasonable fertilization in chestnut orchards.【Method】 Eight-year-old Castanea mollissima ‘Yanshanzaofeng’ in Qianxi County, Hebei Province, China, was used as the research object, and a single-factor randomized block group experiment design was adopted, with six treatments: 100% inorganic fertilizer (C₁), 75% inorganic fertilizer + 25% organic fertilizer (C_0.75O_0.25), 50% inorganic fertilizer + 50% organic fertilizer (C_0.5O_0.5), 25% inorganic fertilizer + 75% organic fertilizer (C_0.25O_0.75), 100% organic fertilizer (O₁), and no fertilization (CK). Soil samples and root samples of 0-20, ≥20-40 cm soil layers were collected by a continuous root drilling method, and the soil physical and chemical properties and root functional traits were measured and analyzed. 【Result】 The treatments affected the physical and chemical properties of the soil to varying degrees. The average organic carbon content of the 0-40 cm soil layer under O₁ treatment was the highest (5.97 g/kg), and the maximum value of total nitrogen content (1.33 g/kg) was found in the 0-20 cm soil layer under treatment C₁. The C_0.25O_0.75 treatment significantly improved the physical and chemical properties of the soil (P < 0.05). The average increase in soil C/N in the 0-40 cm soil layer was higher 38.81% than C₁ treatment and 11.41% than CK treatment, respectively. The average alkaline nitrogen, available phosphorus, and available potassium contents increased by 57.48%, 47.49%, and 32.19% than CK treatment, respectively. The total soil porosity and soil moisture content increased by 11.23% and 13.85%, respectively. Soil bulk density decreased by 11.23% than CK treatment. The combined application of organic-inorganic fertilizer significantly increased the average length density of fine roots, surface density of fine roots, volume density of fine roots, specific root length, and fine roots of 0-1 mm in the 0-40 cm soil layer (P < 0.05). The overall performance was C_0.25O_0.75> C_0.5O_0.5> C_0.75O_0.25. In the 0-40 cm soil layer treated with C_0.25O_0.75, the average density of fine root biomass was the highest (511.24 g/m³), 35.42% higher than that of CK, and 6.00% higher than that of C₁. The ratio of fine root length, root surface area and root valume was significantly increased by applying high proporation of organic fertilizer. Principal component analysis showed that soil properties and root traits all had higher load values on the three principal components than other indicators, and the comprehensive sequence of soil nutrient status and root traits under different treatments was C_0.25O_0.75> C_0.5O_0.5> C_0.75O_0.25> O₁> C₁> CK.【Conclusion】 The organic-inorganic fertilizer combined application treatment (C_0.25O_0.75) effectively improved C/N and soil available nutrients, promoted an increase in 0-1 mm fine roots, and increased the proportion of absorbed roots. Which was a better choice for the fertilization mode of chestnut orchards in Qianxi County, Hebei Province than others.