To investigate the effects of long-term tillage on soil aggregates, soil organic carbon (SOC), and its fractions in black soil regions, this study used no-tillage and long-term tilled soils in spring, summer, and autumn as research objects. Dry sieving and wet sieving methods were employed for aggregate fractionation and determination of stability parameters. Conventional analytical methods were used to measure SOC fractions and other physicochemical properties, followed by redundancy analysis (RDA) and Pearson correlation analysis. The results showed that: (1) After long-term tillage, the mass fraction of large-sized (>1 mm) water-stable aggregates, mean weight diameter (MWD), and geometric mean diameter (GMD) were all lower than those in no-tillage soil, while the fractal dimension (D) and soil erodibility (K) value were higher. With seasonal changes, the mass fraction of large-sized water-stable aggregates, MWD, and GMD in long-term tilled soil gradually increased. (2) Long-term tillage reduced the contents of SOC, readily oxidizable organic carbon (ROC), dissolved organic carbon (DOC), and potentially mineralizable carbon (PMC) compared with no-tillage soil. Seasonally, SOC and light fraction organic carbon (LFOC) contents in long-term tilled soil showed a gradual increasing trend. (3) After long-term tillage, soil moisture content and pH were lower than those in no-tillage soil, while available phosphorus (AP) and available potassium (AK) contents were higher. With seasonal variations, soil moisture content in long-term tilled soil first decreased and then increased; pH showed a gradual decreasing trend; total nitrogen (TN), AP, and AK contents initially increased and then decreased. (4) Pearson correlation analysis revealed that SOC was positively correlated with LFOC; DOC was positively correlated with PMC, ROC, and SOC; the mass fraction of large-sized water-stable aggregates, MWD, and GMD were positively correlated with soil pH and SOC; both pH and moisture content were positively correlated with DOC, ROC, and PMC contents, while AP and AK were negatively correlated with DOC. RDA results indicated that the environmental interpretations of AK, AP, SOC, and pH were 30.4%, 23.2%, 18.8%, and 16.4%, respectively. Collectively, long-term tillage tends to cause soil compaction, reduce soil aggregate stability and the contents of SOC and its fractions. Available potassium, soil moisture content, and pH are the main environmental factors affecting changes in soil aggregates and organic carbon fractions.