This book studies systematically Chinas offshore tropical cyclone strength mutations mechanism. Some of the results and criteria are available for actual business forecast reference. This book starts from the non-linear dynamic-thermal equations, develops dynamic system of tropical cyclones,analyses evolution of system with some physical parameters state (such as the non-adiabatic heating, the static stability, the inertia stability and speed of the vertical shear, level temperature gradient and absolute vorticity) causing the equilibrium instability, and analyzes critical condition of the mutation. At the same time,it puts forward physical parameters that can be used for diagnosis of tropical cyclones strength changes.