The fertility of urban forest soils significantly influences forest quality enhancement. To assess soil fertility status of urban forest land in megacities, this study selected Shanghai as a case. Utilizing a stratified sampling approach, 632 topsoil (0-20 cm depth) samples were collected from 2023 to 2024. Eleven soil fertility indicators were analyzed, including texture (ST), bulk density (BD), and others. And relevant standards from the Second National Soil Survey (such as soil nutrient grading), the modified Nemerow index method, Pearson correlation analysis, and stepwise linear regression analysis were used to evaluate the fertility characteristics, analyze the impacts of administrative districts (Chongming, Pudong, Minhang, Fengxian, Jinshan, Songjiang, Qingpu, Jiading, Baoshan) and forest types (water conservation forest, protective forest, environmental protection forest, open recreational forest, other forests) on soil fertility, and investigate the correlations between soil indicators and fertility, along with their relative influences. The results showed that: 1) ST of urban forest land of Shanghai was predominantly silty loam or silty clay loam. BD was relatively high, and non-capillary porosity was low, with average values of 1.43 g/cm³ and 1.05%, respectively. Soil pH ranged from 4.97 to 9.07, being overall alkaline. Electrical conductivity (EC) was at moderate level, and cation exchange capacity (CEC) was at moderate level, in the range of 3.19-22.6 cmol/kg. Total nitrogen content (TN) was at moderate level, while available phosphorus (AP) and available potassium (AK) contents were at moderate to lower levels, and soil organic matter (SOM) and alkali-hydrolyzable nitrogen (AN) were at deficient level, available phosphorus (AP). 2) Comprehensive evaluation using the modified Nemerow index method indicated that the overall soil fertility of urban forest land of Shanghai was at ‘moderate’ level but partly lower (comprehensive fertility index was 1.15). Forest type had no significant impact on soil fertility, but administrative district significantly affected forest soil fertility. 3) Except for clay content and EC, comprehensive fertility index of urban forest land was significantly correlated with other soil indicators, the correlation coefficients with TN and SOM were relatively high, which were 0.763 and 0.733, respectively. The results of stepwise linear regression analysis showed that SOM, CEC, and TN had the highest standardized coefficients, which were 0.300, 0.263, and 0.256, respectively. In conclusion, soil fertility of urban forest land of Shanghai was moderate but partly lower and influenced by administrative district, and SOM was the key soil constraint factor for improving soil fertility.