Risk analysis and the early warning system for ill reservoir dams is considered as the extending and strengthens of dam safety, including a series of processes of analyses, appraisal and implementation, which can be mainly divided into five fields, the causes mining for the hidden disease patterns of ill reservoir dam, risk analysis, flowchart of the early warning system, the warning sign identifying model, risk reducing and emergency response plan, etc. The main research is as the following:Firstly, the mechanism and the causes for the hidden disease patterns of ill reservoirs are analyzed and the possible hidden disease patterns which can cause to crash are identified, from which the practical crash pattern sets are acquired. Based on the Neumann risk model, a new dam risk fusion method is presented with both qualitative analysis and quantitative analysis methods.Secondly, the expert weight is modified with the ISODATA method and fuzzy synthesis judgment law, which can be used to calcaulate the risk of the dam. The popular acceptable risk appraisal method in other security domains is applied in dam safety field. The acceptable risk appraisal method in dam safety field is studied from the individual, the society, the economy and the environment four aspects.Thirdly, the framework of early-warning system for ill reservoir dam is set up with the Web GIS technology. Based on the above, the classification and the selection and the principle of the early warning index is studied, including the developing method for the index system.Fourthly, the warning sign system and the method to calculate the warning sign index of the two typical dams, earth rock dam and concrete dam, are studied separately. With the help of the modified model by the data fusion theory, the warning sign identifying model for ill reservoir dam for those who have the monitoring data is developed.Finally, a method of the dynamic adjusting of the limited water level is studied based on the risk of the hydraulic structure.The dynamic appraisal system of disaster and the framework of the dam emergency response plan for ill reservoir dams based on the Web GIS technology are designed which are useful to collect the loss data caused by the disaster and can be used to reduce the downstream lose effectively.