Cultivated land ecological security is vital for preventing human–land relationship deterioration, enhancing ecosystem service value, and promoting sustainable development. This study constructed a DPSIR-based evaluation index system and applied an improved TOPSIS method to assess countylevel cultivated land ecological security subsystems in the middle and lower reaches of the Yellow River in 2020. Interactions among subsystems were further analyzed using Pearson correlation and geographically weighted regression to capture both overall and local spatial heterogeneity. The main findings are as follows: (1) The overall level of cultivated land ecological security in the study area remains in a marginally secure and transitional state, and the spatial distribution shows a west-high– east-low pattern. The ranking of subsystem levels is: State > Driving Force > Response > Impact > Pressure. (2) Subsystems are closely and intricately interlinked, such that changes in any single subsystem may trigger chain reactions in others; however, the strength of these correlations varies significantly across subsystem pairs. (3) Subsystem combinations can be classified into global and local correlations. Globally positive correlations include D → P, P ↔ S, P ↔ R, I ↔ S, and I ↔ R. Globally negative correlations include D → I, D → S, D → R, and S ↔ R. Locally autocorrelated combinations include P → D, I → D, S → D, and R → D.