针对相位编码量子密钥分发(QKD)系统中存在的相位漂移和截获-重发攻击，分析了双马赫-曾德尔干涉仪QKD 系统，给出了探测器的输入信号模型, 计算了系统量子误码率及窃听信息量，并为提高密钥生成率提供了一种可能的方法。研究表明，相位漂移会使系统误码率增加，稳定性降低；相比理想的截获-重发攻击，窃听信息量有所下降，因此密性放大过程对窃听信息的估计值可以相对减小，最终密钥生成率得以提高。在不考虑传输光纤中的相位相对漂移时，误码率随相位漂移角度呈余弦变化，全部截获-重发攻击时的变化周期是无窃听时的一半，变化频率更加剧烈。55%部分窃听时，若合法通信者选择误码阈值为15%，窃听者可获得25.5%的信息量且不被发现。

In consideration of phase drift and intercept-resend (I-R) attack, the quantum key distribution (QKD) system based on double Mach-Zehnder interferometers is analyzed, the model of detectors′ input signal is built, and the formulas are presented to describe the relationship between the phase drift angle and quantum bit error rate (QBER), as well as the drift angle and eavesdropping information. Meanwhile, a possible method to increase the key generation rate is proposed. Analysis shows that phase drift causes extra errors and damages the system stability. Compared with I-R attack under ideal conditions, eavesdropping information declines, thus the eavesdropping information estimated by privacy amplification could decrease and the final key generation rate would increase. Regardless of the relative phase drift in transmission fiber, QBER varies with phase drift as cosine function, whose period decreases by half under total I-R attack, meaning more sensitive to phase drift. When eavesdropper chooses to attack 55% of all keys, she can gain 25.5% information undiscovered.