Both the typological classification and the correlation of landslides observed in the area of Shimajiri-mudstone, Okinawa Island is researched. The landslides are classified into the first activated mudstone slides, the quasi-first activated mudstone slides and the re-activated colluvial-soil slides, and also among them have similar systems. The quasi-first activated mudstone slides have existing slide blocks within the lower part of these slide mass, and have the possibility of progressive failure of mudstone which is promoted through the release of stress equivalent to sliding mass. On the other hand, landslides which do not have those the existing slide blocks, are created by the release of insitu stress which is brought with human-induced land alteration.
For 2,100 place which divided 4km×4km basin in the 50m mesh size, dangerous ground estimate technique which combined the three-dimensional saturated-unsaturated flow analysis with the stability analysis of the infinite slope was developed in order to reproduce the infiltration process of the rainfall. In addition, the setting method of estimated formula of soil layer depth and effect of the vegetation was proposed in order to carry out the dangerous ground estimate. Increase and decrease of the dangerous ground by the change of amount of rainfall was able to be simulated, when the calculation was carried out on the basis of actual rainfall data. From the calculation result, 40 places accorded with actual landslides 88 places, and the accuracy became 45.5%.