Abstract: The strength design of cemented backfill must simultaneously ensure stope stability and control the risk of heavy metal leaching. However, the mechanisms of long-term strength degradation and the critical condition for binder dosage remain unclear under prolonged service environments. Accordingly, this study investigates the performance evolution of weakly cemented backfill under chemical erosion, targeting four heavy metals(Pb, Cu, Zn, Cr), through static leaching tests, SEM, and XRD analysis. The results indicate that: ① Cr exhibits the highest stability, followed by Pb and Zn, while Cu is the most susceptible to morphological transformation due to environmental and chemical influences. ② The long-term stability of the backfill is highly dependent on the ambient pH. Specimens with a binder-to-tailings ratio of 1∶10 achieved the highest 90 d strength (2.11 MPa)under neutral conditions (pH=7), whereas those with a 1∶20 ratio showed the lowest strength (0.63 MPa) in an alkaline environment (pH=10). Acidic conditions induced early-stage erosion, while alkalinity led to late-stage expansion and degradation. ③ The binder-to-tailings ratio significantly influences the immobilization efficiency. The highest leaching concentrations for Pb, Cu, Zn, and Cr were observed at the 1∶20 ratio, measuring 0.000 95, 0.94, 0.86, and 0.014 7 mg/L, respectively—approximately 2 to 3 times higher than those at the 1∶10 ratio. Despite this increase, all values complied with the Class III standards of the "Quality Standard for Groundwater" (GB/T 14848—2017). This research clarifies the interrelationships among environmental conditions, mix proportion, and backfill performance, providing a critical basis for the design of backfill in green mining.