[Objective] Chestnut is an important economic crop in China. However, in earth-rocky mountainous area of northern China, where there are significant chestnut production regions, severe soil erosion problems often occur under the chestnut forests. Therefore, it is meaningful to quantitatively evaluate soil erosion and soil quality in this area. [Methods] From 2022 to 2024, a survey was conducted on twelve indicators like soil erosion modulus, soil particle size distribution, organic matter, and total nitrogen in the soil under the chestnut forests and the surrounding shrub forests in the Zhujiawan and Badaohe watersheds of Miyun and Huairou Districts in Beijing. Soil fertility, degree of soil coarsening and erosion intensity were analyzed, and the soil quality index (SQI) was evaluated by principal component analysis (PCA). [Results] (1) The annual average soil erosion modulus of chestnut forest without measures was 8.3 times higher than shrub forest. From 2023 to 2024, the rill erosion modulus of chestnut forest after flood season was more than 13000t/km2, and the understory erosion was very intense. (2) The content of coarse sand (0.5-2mm) in the surface 1cm soil of chestnut forest was higher, and its average value was about 1.3 times higher than adjacent shrubs, indicating a tendency of soil coarsening. (3) The average value of organic matter, total nitrogen and alkali-hydrolyzed nitrogen in the soil of chestnut forest was less than a quarter of that of adjacent shrub, the average value of available potassium was about half of that of adjacent shrub, and there was enrichment of available phosphorus and slow-available potassium. (4) The SQI value of chestnut forest was significantly lower than that of shrubland (P=0.025<0.05). [Conclusion] The soil under the chestnut forests in the earth-rocky mountainous area of northern China suffers from severe erosion, soil coarsening and nutrient loss, and its quality is poorer than that under the surrounding shrub forests. Scientific land management measures need to be implemented. This research can provide a theoretical basis for the study and management of soil and water conservation under economic forests in the earth-rocky mountainous area of northern China.