The invention discloses a full-duplex relay selection method based on perfect channel state information and solves the defect that the existing relay selection technology does not consider leakage noise link channel state information. The method comprises the following specific steps of (1) estimating forward link channel state information of a relay node; (2) estimating leakage noise link channel state information; (3) estimating loop interference channel state information of the relay node; (4) estimating backward link channel state information of the relay node; (5) obtaining all channel state information through a destination node; (6) computing an instantaneous signal to noise ratio at the destination node; and (7) selecting a relay. According to the method, when the relay is selected, the relay node capable of maximizing the instantaneous channel capacity of a system is selected, and the method has the advantages that the interruption probability of a full-duplex system is reduced and the reliability of a full-duplex cooperative communication system is improved.