Abstract: The traditional tracking differentiator can only track the input signal in first-order indi-scrimination degree. This article proposes the cascade form of third-order tracking differentiator with α-order indiscrimination degree based on α-order linear tracking differentiator. The minimal realization dimension of the presented third-order tracking differentiator with α-order indi-scrimination degree is 2α. According to the minimal realization forms, the estimation value of input signal and its each order differential signal could be directly achieved. Simulation experi-ments show that the differentiator can increase the abilities of tracking higher order input signal.