本文用149次地震资料拟合出宁夏所属台网各台由振动持续时间求算震级M_D的公式,给出了各台M_D公式中的系数α,β,并讨论了当震级M_L≥5.0时持续时间“短缺”或饱和的原因。经统计检验,由持续时间测算的震级M_D比用最大振幅测算的震级M_L的残差减小一倍多,即精度有明显提高。 In this paper, 149 seismic data are used to fit the formulas of magnitude M_D calculated by vibration duration of each station in Ningxia, and the coefficients α and β in each M_D formula are given. It is also discussed that when M_L≥5.0, Time “shortage” or the reason for saturation. The statistical test shows that the magnitude M_D measured by duration is more than doubled as the residual magnitude of the magnitude M_L estimated by the maximum amplitude, that is, the precision is obviously improved.