This study aims to evaluate the environmental stability of a backfill material composed of fly ash, low-grade limestone, and green cement by conducting short- and long-term leaching assessments. The short-term leaching tests were based on the Korean Standard Leaching Test(KSLT) and the Toxicity Characteristic Leaching Procedure(TCLP) protocols, and all measured parameters satisfied the leaching standards of the Waste Management Regulation. Although the total Cr and As concentrations exceeded the drinking water quality standards in some samples, this does not indicate regulatory non-compliance for ground backfill, which was assessed against the KSLT/TCLP leaching limits that were met under the test conditions. For long-term behavior prediction, geochemical modeling was performed using pH-Redox-Equilibrium in C programming language(PHREEQC). The leaching concentrations of the major heavy metals(Pb, Cd, Cu, and Zn) were predicted to be below 0.010 mg/L, indicating stable concentrations under highly alkaline conditions. This study provides data supporting the long-term application potential of mine backfill materials that utilize industrial byproducts.