Abstract: On May 20, 2010,the hidden potential geological hazard was found at the back hill of Qishan in Yongtai County of Fujian Province.Many group openings and fissures of 35cm to 80cm long were found at the lower part of the hill side.Huge collapses were happening continuously.The size of the sliding rock mass is about 80000m3. The risk of subsequent landslides is high.Any such landslide could cause disasters to the 2565 local residents and approximate 538million properties below the hillside slope. This paper presents the detailed investigation on the basic characteristics of the slip mass and preliminary analysis of the disaster causes.The investigation is based on the massive geologic investigation into the site of the disaster.It includes in-situ measurement,monitoring and other methods.The results indicate that the relatively prominent terrain condition of the source area and the characteristics of the geotechnical mass are the fundamental conditions for the occurring of the slope instability and potential huge landslides.The saturated surcharge of the rainfall,and the rainfalls infiltrating and softening effect along the joint fissures directly caused the slope instabilities and the potential landslides.Moreover,the paper sets forth some urgent remedial advice and unloading measures according to the features of the landslides.Finally,the monitoring results are analyzed and can used to direct the unloading construction.Therefore,the safety of the construction and the lives and property were all guaranteed.The successful case provides scientific evidences to direct urgent handling of geological disasters that would happen in Fujian littoral area.