根据两台独立激光器拍频的理论模型，计算得到了洛伦兹线型和高斯线型的拍频线宽随衰减值的变化关系。为了提高激光线宽测量精度，在未知拍频线型时应选取较小的衰减值计算激光线宽；在已知拍频线型的情况下可选取较大的衰减值计算激光线宽。实验上采用窄线宽半导体激光器拍频测量其激光线宽，根据几个特殊衰减值处的线宽比值关系来判别拍频线型。选用较大衰减值处的拍频线宽计算激光线宽，测量结果与仪器出厂指标相比，误差仅为0.23%。该方法对其他线型仍然适用。

Based on theoretical model of beat frequency using two independent lasers, beat frequency linewidths of Lorentz and Gaussian linetypes changing with different attenuation values are obtained theoretically. It is significant that smaller attenuation value should be chosen to calculate laser linewidth if laser linetype is unknown previously and larger attenuation value for known laser linetype. In the experiment of beat frequency using two external cavity diode lasers (ECDL), linewidth ratio is measured under typical attenuation values, which can be used to judge linetype of laser. Using the method above, linewidth of laser is achieved with an error about 0.23% compared with its calibration data, therefore linewidth measurement precision of laser is enhanced. The method is still applicable to other linetypes analysis.