The main purpose of the book is to present the theory and research method about the collapse of the unsaturated soil bunding for the scientific researchers, the engineers and technicians, and to provide the theory support for the actual project. This book suits in the hydraulic engineering, the ground project and the related domain scientific researchers, the engineers and technicians. There are six chapters. Chapter 1 covers the research situation in the world, special in China, and the research thought and the frame. Chapter 2 concerns the water movement of unsaturated soils. Chapter 3 presents the shear strength of unsaturated soils under the seepage. Chapter 4 describes the decay model of the riverbank stability. Chapter 5 discusses a special collapse type: the incline free face riverbank collapse. Chapter 6 deals with the continuous model of three stage collapse. The book is supported by the National Natural Science Foundation of China (Grant No.50709015), China Postdoctoral Science Special Foundation (Grant No.200801081), and China Postdoctoral Science Foundation (Grant No.20070410531).