This article is to do the quantitative analysis on digital trigger resolution, digital detected speed device. CPU calculation and word bits. And its selection of pulse light generator of P value according to the demand of systematic controlling accuracy. 根据系统稳态控制精度的要求,对数字触发器分辨率、数字测速装置、CPU运算等字长和光电码盘P值的计算选择做了定量分析,并对M/T法测速存在的缺点提出了改进方法。