The decoy-state quantum-key-distribution method (based on a heralded single photon source) is frequently used in experiments serves as an object of study. Using the finite data, it is possible to derive the formula of the lower limit of the single-photon state and the upper limit of the error rate and to obtain the lower limit of key generation rate with unconditional security and the range of secure transmission distance. According to the conclusion drawn from the research, the unconditional security boundary of decoy-state quantum key distribution will be obtained if the number of data-set size is known. The number of transmitted data can also be decided according to the demands for quantum key distribution. In this way, the loop holes in security which are created by finite data can be avoided so as to improve the security and efficiency of quantum key distribution.%以实验中采用最多的诱骗态量子密钥分配方案(基于预报单光子源)为研究对象,在有限数据条件下,推导了单光子态计数率下限和误码率上限的计算公式,得出了无条件安全密钥生成效率的下限和安全传输距离的范围.根据研究结论,只要已知系统发送数据数量,便可得出量子密钥分配无条件安全界限；也可以按照密钥分配的指标要求,反过来确定系统发送数据的数量.这样避免了数据有限带来的安全漏洞,提高了实际量子密钥分配的安全性和有效性.
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