The prediction of landfill settlement is very important for managing land properly, especially in small national land like Korea. It is difficult to express settlement using the consolidation theory because biochemical decomposition is main reason of settlement, and organic materials in landfill are decomposed far long time. In this study, LFG (Landfill Gas) generation characteristics are studied to find long-term settlement analysing model landfills. Two lysimeters are made; one is leachate recycled, and the other is not leachate recycled. The relationship between gas generation and settlement is analysed as a function of time. A mathematical gas generation model is suggested to predict long-term settlement due to biodegradation, and correction coefficient is recommended for long term settlement through model tests. The leachate recirculation system is more effective to accelerate landfill settlement. The appropriate coefficients of gas correction for non-recycled leachate model are 1.4 and 1.7 for recycled system from tests showing 22% of acceleration.