In quantum key distribution systems, bright light blinding attack makes use of the detection characteristics of linear mode caused by bright light in the actual work of single-photon detectors to control the output of single-photon detectors to be 0 or 1, so as to implement key stealing. To address the potential vulnerabilities of the new type of pulse illumination attack scheme proposed by previous researchers, a defense scheme against the detector blinding attack by pulse illumination based on beam split detection is presented. Based on the countermeasures of detecting the working current of the device to judge whether there is a blinding attack, this scheme realizes the detection of bright light pulse with 100% probability before the detector is blinded, therefore, it can close the detection loophole of pulse illumination attack and improve the security of quantum key distribution systems.