Abstract: Unregulated landfill sites largely use natural conditions to fill out the untreated garbage and take over lots of land resources.They not only affect the city environmental sanitation,but also pose significant risks to resident domestic water.Because there are many unregulated landfill sites in Beijing,the needed funds for treating all of them are huge.Therefore,preliminary survey and assessment on the unregulated landfill sites are urgently needed to provide the scientific basis for government decision precedence order and choice of technical treatments.Survey and assessment on unregulated landfill sites have a remarkable difference with traditional geotechnical investigation,especially in the areas of required investigation,prospecting technique,exploration of arrangements,and inspection and testing projects.China has not yet enacted domestic standards and guidelines about the preliminary survey and assessment on unregulated landfill sites.The risk assessment method and the indicator system are established first in this papers.They combine the ground water pollution risks and dangers of garbage itself by hierarchy process method.Also the concepts of anti-contamination effective thickness and anti-contamination index are first put forward.Finally,this paper takes a project in Beijing as an example.It discusses the actual application of the risk assessment method,and summarizes systematically the procedures and techniques for survey and assessments. The practical results show that the proposed preliminary survey and method assessment have important reference value to similar unregulated landfill survey.