Chaos theory is applied to electronic defiance. The approaches of chaos attacking and interfering optical fiber communication systems are proposed. Two methods of chaos masking attacking(CMAT)and chaos phase attacking(CPAT)are presented. In CMAT,the larger chaotic signal can mask straightway message signals and the small chaotic signal can interfere message signals to add bit-error-rate by state superposition principle. In CPAT,the chaotic signal can overprint the phase of the message signals by the cross-phase modulation so that chaos can interfere message signals. At last,optical fiber communication system at wavelength 1.31 for bit rates of 2.5 Gbit/s,5 Gbit/s and 25 Gbit/s are effectively attacked by CMAT and CPAT in simulations.