[Objective] Soil quality of plantation forests in the north China Plain was quantitatively evaluated， in order to provide a scientific basis and references for the related soil quality improvement and limiting factor diagnosis in the region. [Methods] Populus spp. plantations with different densities （i.e.， 1 111， 833， 625， 555， and 416 trees/hm²） were taken as cases. Soil samples were collected from the 0—20 cm depth layer of the soil in poplar forests in late October， 2024. The main physicochemical soil properties and related enzymatic activities were analyzed. The minimum dataset was selected based on principal component analysis. Soil quality was evaluated using the soil quality index and limiting factor diagnosis. [Results] ① Based on the principal component analysis of the total dataset， a minimum dataset was established， consisting of soil total carbon， sucrase activity， electrical conductivity， silt content and available phosphorus. ② The soil quality indices of poplar plantations with different densities were ranked as follows （trees/hm² ， followed by values in brackets）： 416 （0.55） > 555 （0.51） > 625 （0.49） > 1 111 （0.48） > 833 （0.44）. Stand density significantly affected the soil water content， pH value， organic carbon， total carbon and available nutrient values. ③ Soil quality limitations in the study area were primarily moderate and mild. Soil organic carbon （15%） and water contents （13%） were the most significant soil quality-affecting limiting factors. All poplar plantations faced limitations related to soil nutrient and water availabilities. [Conclusion] Soil quality was optimal in poplar plantations at a density of 416 trees/ hm². All poplar plantations in the north China Plain face challenges of insufficient soil nutrients and water scarcity. Therefore， developing scientific fertilization and irrigation management practices and determining appropriate afforestation densities in plantation practices would be essential to achieve sustainable soil utilization.