Landslide is one of the natural disasters cause damage to life and casualties in Thailand every year. A number of factors trigger the landslide including heavy rainfall during tropical monsoon, geological condition, and change of land uses. Prediction and warning by Geotechnical Engineering Method is the direct method for calculating the Factor of Safety (F.S.) of soil slope during heavy rainfall. Since, the strength of unsaturated soil is changed during the water infiltration in soil mass. Metric suction related to the volumetric water content in soil mass can be analyzed for each rainstorm patterns. Field monitoring can be confirmed by using tensiometer for pore pressure and moisture content measurement to verify the infiltration modeling. By applying the infinite slope stability analysis into geographical information system (GIS) approach, the prediction of landslide on Phuket area is given in term of the critical rainfall envelope. This method has the potential application for real time monitoring and warning in the future when the measuring rainfall intensity is reported from the automatic rain gage in the field. Then slopes stability condition can be calculated simultaneously and reported back for the further warning.