[Objective] Dry–wet cycles can disrupt soil structure and reduce soil stability, and are recognized as an important driving factor in the rapid development of erosion gullies. To clarify the differences in erosion resistance among soil layers on gully sidewalls under dry–wet cycling, this study conducted experimental analyses on typical gully walls in the black soil region of Northeast China and examined the influence of dry–wet alternation on gully erosion processes. [Methods] Soil samples were collected from gully sidewalls of cultivated land in the black soil region at depths of 0–30 cm, 30–60 cm, and 60–90 cm. A laboratory-simulated dry–wet cycling experiment was conducted to determine soil mechanical composition, water-stable aggregates (WSA), soil disintegration rate (SDR), and soil anti-scour coefficient (ANS). Differences and variation patterns in erosion resistance among the three soil layers were analyzed and compared. [Results] Dry–wet cycles significantly affected WSA, SDR, and ANS in all three soil layers. After one cycle, dry–wet alternation exerted generally positive effects, with aggregate breakdown rate (PAD) decreasing by 0.23%, 7.28%, and 0.43% in the 0–30 cm, 30–60 cm, and 60–90 cm layers, respectively. Meanwhile, the anti-scour coefficient increased by 171.03 L.g?1 in the 0–30 cm layer and by 287.84 L.g?1 in the 30–60 cm layer. After five cycles, the strongest response occurred in the 0–30 cm layer, where SDR increased by 72.29 g.s?1, while in the 60–90 cm layer, PAD increased by 1.33% and SDR decreased by 6.1 g.s?1. After eight cycles, PAD increased by 4.315% and 7.78% in the 0–30 cm and 30–60 cm layers, respectively. Overall, WSA in the 0–30 cm layer decreased and SDR increased markedly with increasing cycle number, although its relatively high organic matter content helped maintain strong resistance to scouring. The 30–60 cm layer exhibited improved water stability after one cycle, indicating temporary structural enhancement; however, structural degradation and reduced anti-scour resistance occurred after 5–8 cycles, although resistance to disintegration remained higher than the initial state. The 60–90 cm layer showed poor water stability, high SDR, and weak anti-scour capacity, and its structure was difficult to recover once damaged. [Conclusion] Dry–wet cycles intensified the vertical differentiation of erosion resistance along gully sidewalls, with the surface layer remaining relatively stable, the middle layer exhibiting pronounced fluctuations, and the deep layer being the most vulnerable. This process promotes gully wall collapse and accelerates gully expansion, providing important implications for soil and water conservation and gully erosion control in black soil regions. Management strategies should therefore emphasize structural improvement and enhancement of anti-scour capacity, particularly in the middle and lower soil layers.