The invention provides a security monitoring method for an electric vehicle range increase system. The security monitoring method is safe and reliable and includes the four steps of generator mode monitoring, engine torque monitoring, generator torque monitoring and engine speed monitoring. A vehicle control unit is used for monitoring generator modes, engine torque, generator torque and engine speeds, safe operation of the electric vehicle range increase system is guaranteed, an electric vehicle can automatically quit from a range increase mode when the range increase system breaks down, and security of the electric vehicle is protected.