Two factors affecting covert tapping are first investigated by deducing the fiber bending loss formula.Then on this basis

the framework of the tapping system is designed

a fiber-optic experimental tapping system set up

covert tapping realized and the optimal bending radius value for realizing covert tapping gained.Finally

considering the features of covert tapping

and making use of the fact that the bending loss of long wavelength signals are much greater than that of normal communication wavelength signals under the same conditions

an effective tap detection method is proposed with improved system detection sensibility.