The invention relates to a method and a system for quantum communication security. An Alice terminal comprises a watchdog detector, an optical attenuator, a phase modulator, a reflector, a controller and a photon emitter; and a Bob terminal comprises a laser, a time division multiplex / demultiplex system, a phase modulator, a single photon detector, a controller, an optical switch and a reflector. The method and the system have the advantages that: (1) the two-way, stable and safe distribution of quantum keys is realized, the polarization and phase change of a single photon can be automatically compensated, and the aim of stable long-distance transmission is achieved; (2) the Alice terminal adopts the watchdog detector, on one hand, Trojan attack and intermediary attack can be detected by measuring the number of weak pulses reaching or leaving the Alice terminal, so that the communication security is improved greatly, and on the other hand, the communication speed and communication distance of the system are improved greatly; and (3) the Alice terminal and the Bob terminal can be adjusted and corrected respectively, can select mu independently without transmitting photons by means of unsafe optical fiber lines so as to ensure the system security.