Landfill gases (LFGs), which consists of sulfur compounds, odorous substances such as ammonia and amines, and volatile organic compounds (VOCs), is generated during the natural process of bacterial decomposition of organic material contained in municipal solid waste (MSW) landfills. The VOCs in the LFGs cannot be only decomposed easily into the soil after landfilling but they also can cause serious problems for the surrounding atmosphere, soil, and groundwater because of their toxicity. Moreover, VOCs have been identified as precursors of photochemical smog and they are toxic and carcinogenic chemicals. Furthermore, VOCs comprise a low rate of the emissions, but they can cause cancer. Therefore, it is important to evaluate the hazard causing by VOCs in LFGs. This study is aim to identify chemicals in LFGs and the hazardous evaluation by mixing between chemicals in LFGs. The selected landfill site in the study is located in Daejeon. Waste generation data were obtained from the Ministry of Environment (MOE) of South Korea. To evaluate the amount of the selected VOCs (47) among the primary disintegration models, LFGs generation model in LandGEM program was used. For the gas mixing reaction, a program called CRW 4.0 was introduced by the NOAA in the United States was used. As a result, the cumulative capacity of landfills in 2015 was estimated at 7,650,682 tons. Therefore, the total LFGs generation in 2015 was 7.717 × 107m³. Also the LFGs showed almost all the hazardous reactions with NOx and O3 in the atmosphere. As VOCs in LFGs mixed air emissions, we confirmed that toxic potential gases such as phosgene, hydrogen halides, halogenated organics, chlorinated amines and acidic fumes are generated.