The invention discloses a method and a device for detecting the strong light blindness attack by a quantum key distribution system. The method comprises the following steps of: preparing an auxiliaryparticle which interacts with the quantum state of the code particle; receiving the code particle sent by a sender to enable the auxiliary particle to interact with the code particle; respectively detecting the quantum state of the code particle and the auxiliary particle; calculating the bit error rate of the code particle and the bit error rate of the auxiliary particle according to the detection result of the code particle and the detection result of the auxiliary particle; judging whether the bit error rate of the auxiliary particle is larger than the preset auxiliary particle threshold value or not; and judging that a strong light blindness attack exists in the communication process when the bit error rate of the auxiliary particle is larger than the preset auxiliary particle threshold value. According to the method for detecting strong light blindness attack by a quantum key distribution system, the eavesdropper cannot control the single-photon detector of the auxiliary particlesince the auxiliary particle is not transmitted in the quantum channel, so that whether the quantum communication is subjected to strong light blindness attack or not can be effectively judged by detecting the bit error rate of the auxiliary particle.