Numerous artificial slopes emerged in the watersheds of the Chinese Loess Plateau (LP) after the Gully Land Consolidation project (GLCP) that cut slopes to create farmland in the gully, which had incurred instabilities over time and could potentially resulted in soil erosion and geological hazard. This paper explored the characteristics and prevention mechanisms of artificial slope instability after the GLCP with field investigation in a typical watershed and the Back Propagation Neural Network (BPNN) method. The results showed that: (1) 439 instabilities induced by infiltration and erosion were found in 79 artificial slopes. (2) The difference of soil moisture and failure mode resulted in the instability degree of shady slope and lower slope were significantly higher than that of sunny slope and upper slope. (3) Among the surface condition factors, slope instability volume was significantly influenced by gradient, soil compactness, height and soil shear strength. Platform instability volume had great connection with soil compactness and its shear strength. (4) A “Drain-Improve-Green-Reinforce (DIGR)” system was proposed as the prevention mechanism for artificial slope instability, which included drainage system, soil improvement, vegetation protection, and reinforcement engineering. Taken together, this research provides the scientific reference for a better understanding and prevention of artificial slope instability, which would contribute to ensuring GLCP effectiveness and ecological security in the LP.