Abstract: On the issue of overlappnig problem of European standard DIN EN 10049—2006 adopting 2.5 mm long wave tliter cut-off wavelength to measure the surface roughness Ra of cold rolled steel sheets and GB/T 2523-2008 adopting 0.8 mm short wave tiiter cut-off wavrlength and 8 mm long wave tiiter cut-off wavrlength to measure the surface waynness Wa， systematic measurement of Ra and Wa of stochastic surface cold rolted steel sheets was done staring from the nrterpretation of Ra and Wa.The reason of that the measurement accuracy didn't nncreased with the mcrease of the transmission band wddth between the short wave and the long wave for the steel sheets with Ra< 2 μαη，was analyzed by niterpreting the principte of the filter transmission band which completing the measurement. The method of increasing samping rnterval numbers from 5 to 16 to make the evaluation tength nncrease from 4 mm to 12.8 mm was raised and vetitied on the basis of 0.8 mm cut-off wavrlength of ISO 4288-1996，as a solvrng method to coinaide to the 12.5 mm evaluation tength of DIN EN 10049-2006.