分析比较了星地量子密钥分发系统中由于大气湍流和大气色散导致的脉冲展宽。分别推导了大气湍流和色散效应下脉冲展宽比。根据大气压强和温度与海拔间的实测数据，计算了到达脉宽与不同初始脉宽、工作波长、链路天顶角的关系。并根据到达脉宽计算了系统背景噪声量。数值模拟结果表明：当工作波长为1.06 μm，初始脉宽为15 fs时，到达脉宽有最小值。对于不同的链路天顶角，在无月晴朗的星空，探测器探测到的背景噪声约为1.9×10-10~2.7×10-10，而误码率约为0.5×10-5。

The temporal pulse broadening of cohered laser pulse caused by atmospheric turbulent and dispersion is analyzed. The expression of turbulence-induced and dispersion-induced pulse broadening is given. Based on the measured data of atmospheric parameters and the fitting formula, the relations of pulse broadening to the zenith angle, original pulse and the wavelength of optical signal are obtained．The background noise in satellite-earth quantum key distribution is simulated. The simulation shows that when the wavelength is 1.06 μm and the original pulse is 15 fs, the final pulse has the minimum. For different zenith angle, the background noise is about 1.9×10-10~2.7×10-10, and the quantum error bit rate is about 0.5×10-5.