The change of soil organic carbon (SOC) and nitrogen is vital to farmland ecosystem sustainability after conversion of slope cropland to terrace. Terraces of different ages were selected as subjects to investigate the evolution rule of SOC and nitrogen on the Loess Plateau. The results indicated that SOC density increased from 0.8 kg/m² to 1.2 kg/m² in 30-year terrace in 0-20 cm soil layer and total nitrogen (TN) density increased by 75%. SOC and TN density increased significantly at the initial stage of terraces, and the average accumulation rates were 317.7 and 37.4 kg/(ha·a), respectively. SOC and TN density have exceeded the levels in slope cropland in 10-year terrace and greatly improved (by 74.0% and 107%, respectively) after 30 years,. The greatest soil nutrients and enzyme activity occurred after 30 years. SOC positively related to TN, clay and enzyme activity, while the relationships between SOC and bulk density, pH, and EC were negative. Nitrogen was the major limiting factor of SOC sequestration. Soil environment of long-term use terrace would improve the ability of soil to collect carbon and nitrogen. Terrace has great significance to cropland quality improvement, food security and greenhouse gas emission reduction on the Loess Plateau.