Abstract: Cocamidopropyl hydroxyl sulfobetaine (CHSB) is one of the most promising foaming agents for high-salinity reservoirs because the salt in place facilitates its foam stability, even with salinity as high as 2 × 105 mg/L. However, the synergistic effects between CHSB and salt have not been fully understood. This study utilized bulk foam tests and thin-film interferometry to comprehensively investigate the macroscopic and microscopic decay processes of CHSB foams with NaCl concentrations ranging from 2.3 × 104 to 2.1 × 105 mg/L. We focused on the dilatational viscoelasticity and dynamic thin-film thickness to elucidate the high-salinity-enhanced foam stability. The increase in dilatational viscoelasticity and supramolecular oscillating structural force (ΠOS) with salinity dominated the superior stability of CHSB foam. With increasing salinity, more CHSB molecules accumulated on the surface with a lower diffusion rate, leading to high dilatational moduli and surface elasticity, thus decelerating coarsening and coalescence. Meanwhile, the number density of micelles in the thin film increased with salinity, resulting in increased ΠOS. Consequently, the energy barrier for stepwise thinning intensified, and the thin-film drainage slowed. This work conduces to understand the mechanisms behind the pronounced stability of betaine foam and can promote the widespread application of foam in harsh reservoirs.