The invention relates to a secret communication system based on double chaotic modulation, and the system comprises: a transmitting end which comprises a first chaotic laser which is connected with acoupler, wherein the coupler is connected with a first isolator, the first isolator is connected with a photoelectric switch, a second chaotic laser is connected with a second isolator, and the secondisolator is connected with the photoelectric switch; a receiving end which comprises a third chaotic laser which is in communication connection with a circulator, wherein the circulator is in communication connection with a second photoelectric detector, the second photoelectric detector is in communication connection with a cross-correlator, the cross-correlator is in communication connection with a first radio frequency amplifier and a decision device, and the first radio frequency amplifier is in communication connection with the first photoelectric detector; and a circulator which is in communication connection with the coupler, wherein the photoelectric switch is in communication connection with the first photoelectric detector. According to the invention, double chaos is utilized tospread spectrum of digital information, identical chaotic sequences are synchronously generated, and after the sending end receives information modulation, the receiving end utilizes synchronous local signals to demodulate the information, so that secret communication is realized.