This study investigates the selective depression mechanism of sodium polyacrylate (PAAS) on the flotation separation of smithsonite and calcite using a ternary collector system (Al-BHA-NaOL, (ABN). Micro-flotation experiments were conducted to evaluate the efficacy of PAAS in enhancing separation selectivity. To elucidate the underlying depression mechanism, a series of analytical techniques was employed, including zeta potential measurements, X-ray photoelectron spectroscopy (XPS), contact angle analysis, and scanning electron microscopy (SEM). The flotation results demonstrated that under mildly alkaline conditions, the ABN collector alone exhibited limited selectivity due to the high floatability. Upon the introduction of PAAS, the flotation recovery of calcite decreased significantly, while smithsonite remained largely unaffected, thereby achieving efficient separation. Zeta potential shifts indicated a stronger adsorption of PAAS onto the calcite surface compared to smithsonite, a finding further corroborated by surface wettability changes. XPS and SEM-energy dispersive X-ray spectroscopy (EDS) analyses confirmed the formation of stable complexes between the carboxyl groups of PAAS and calcium sites on the calcite surface. This targeted interaction effectively hindered ABN adsorption, leading to the selective depression of calcite.