The invention is applicable to the technical field of communication, and provides a self-adapting filter, a filtration method and a repeater, wherein the self-adapting filter comprises a filtration module and a tap coefficient updating module, the filtration module is used for the delay decomposing of an input signal u (n) of a transmission antenna and generating a difference output signal e (n); and the tap coefficient updating module is used for obtaining the tap coefficient of the next moment according to the difference output signal e (n) and adjusting the tap weight of an updating filtration device through the tap coefficient. In the embodiment of the invention, the self-adapting filter comprises the filtration module and the tap coefficient updating module, wherein the filtration module is used for the delay decomposing of the input signal u (n) of the transmission antenna and generating the difference output signal e (n), the tap coefficient updating module is used for obtaining the tap coefficient of the next moment according to the difference output signal e (n) and adjusting the tap weight of the updating filtration device through the tap coefficient, and thereby the invention solves the problem that when the tap coefficient of the filtration device is updated, the complicated complex multiplication operation consumes a great quantity of hardware resources and the delay time of the hardware is too long.