国家标准规定以中线为测量基准线评定Rz参数值．但有些资料认为在用光学仪器测量Rz值时，可采用平行于中线的任一直线作基准线进行测量．这造成测点的选取往往与标准定义不符，测量结果受主观影响较大。本文对Rz值的测量进行了研究，通过采用不同基准线恻得Rz值的比较、分析．得出对Rz值的测量必须按国家标准规定的以中线为基准线进行测量的结论．并给出了正确的取点方法． The national standard specifies the Rz parameter value based on the midline as the measurement baseline. However, there are some data that when measuring Rz values ​​with optical instruments, you can use any line parallel to the center line as the baseline. This results in the selection of measuring points is often inconsistent with the standard definition, the measurement results by the subjective impact. In this paper, the measurement of Rz value has been studied, through the use of different baseline Rz value obtained by comparison, analysis. It is concluded that the measurement of Rz value must be based on the national standard as the baseline to measure the conclusion. And gives the correct way to take points.