The invention discloses a secret optical fiber communication system. In the system, a signal output end of a signal sending end is connected with a signal input end of a sending end encryption module;a signal output end of the sending end encryption module is connected with a signal input end of a receiving end decryption module via an optical fiber link; a signal output end of the receiving enddecryption module is connected with a signal receiving end; a signal output end of an initial chaos laser generation device is respectively connected with signal input ends of a sending end chaos laser generation device and a receiving end chaos laser generation device; a signal output end of the sending end chaos laser generation device is connected with a control signal input end of the sendingend encryption module via a sending end photoelectric detector; and a signal output end of the receiving end chaos laser generation device is connected with a control signal input end of a receiving end description module via a receiving end photoelectric detector. According to the secret optical fiber communication system, synchronous encryption signal and decryption signal can be generated by the signal sending end and the signal receiving end, so that a stealer cannot crack a system structure even through the stealer knows the system structure.