The calcium leaching resistance of bonding interface between engineered cementitious composite (ECC) and existing concrete is a key issue in reinforcement engineering. A nitric acid solution of 0.5 mol/L was used to carry out the accelerated leaching test, and the time-dependent influences of interface treatment methods (i.e., roughening, wet saturation and interfacial agent) were investigated via indications of bonding strength, leaching depth and cumulative leached calcium ion. The improvement mechanism in micro scale was analyzed by scanning electron microscopy. The results show that the three interface treatment methods can effectively improve the bonding quality, and their time-dependent influences are similar. The bonding strength before leaching can be used to evaluate the leaching resistance of bonding interface. Roughening is more effective to improve the initial bonding strength, while interfacial agent is helpful to slow down the deterioration rate of interface treatment effect in the leaching process. The improvement effect of combined treatment methods is better than that of single treatment method.