【Objective】Soil organic carbon and nutrients are important indicators of soil fertility. The study on rules of the temporal variation of soil fertility is of important theoretical guiding significance to improving soil fertility and maintaining sustainable development of the agriculture. 【Method】Based on the data of the Second National Soil Survey in 1980 and the soil sampling in 2002, soil samples (0-15 cm) were collected from three soil layers (0-10, 10-20 and 20-40 cm) at the same 26 sampling sites in paddy fields of Yujiang County in 2017 for analysis of soil organic carbon, nutrients, pH and CEC, and comparison was performed for rules of the variation of soil fertility in the past 40 years. 【Result】 The contents of organic carbon, total nitrogen, available phosphorus and available potassium in the upper surface paddy soil (0-10 cm) in Yujiang County was (27.3±1.3) g·kg^-1, (2.9±0.2) g·kg^-1, (40.5±3.8) mg·kg^-1 and (148±7.9) mg·kg^-1, respectively. Compared with the data in 1980, organic carbon and soil nutrients have significantly improved; especially organic carbon, total nitrogen and available potassium in the 0-10 cm soil layer of the paddy fields have increased by 35%, 40% and 34%, respectively, in the past 15 years since 2002. The available phosphorus content in the 0-10 cm soil layer did not change much, while it did increase by 56% in the 10-20 cm soil layer. Compared with the data obtained in 2002, pH in the 0-10 cm, 10-20 cm and 20-40 cm soil layers decreased significantly, while CEC did reversely.【Conclusion】Long-term paddy cultivation applied with chemical fertilizer significantly increased soil organic carbon, nutrients and CEC, but decreased soil pH, especially in the past 15 years.