Establishing warning systems and evacuating inhabitants are recognized as important approaches for disaster risk reduction. While the rainfall-based warning model of landslide or debris flow disasters has been extensively investigated, the problems of implementing the rainfall-based warning model during typhoons or heavy rainfall have received less attention. This study evaluated the warning systems for debris flows and slope failures in Taiwan and Japan. We discuss the characteristics of the warning models and warning issuing systems in Japan and Taiwan, and also suggest evaluation indexes of warning effectiveness: the warning hit rate, false alert rate, warning cover rate, and remaining time for evacuation. In addition, this study focuses on the lack of attention to current rainfall-based warning models during actual disaster cases and several years of statistical data. Finally, this research recommends future disaster prevention strategies and resolution.