Cascading trip-off of wind turbine generators is one of the new problems with the fast development of wind farm clusters. Aiming at the cascading trip-off failures frequently occurring in China， this paper makes a preliminary research. Firstly， the typical development process and time-spatial frame of the failures are analyzed. Furthermore， a prototypical system with wind farm clusters is constructed， based on which， the mechanism of common mode tripping and some dominant factors in the failure evolution are studied. Finally， based on the topology structure and parameters of an actual power grid in China， the cascading trip-off failure is simulated. Some countermeasures are discussed from two aspects: enhancing the voltage stability of the power grid under heavy load condition and improving the operation modes of the doubly fed induction generators.