Abstract: Taking the stainless steel surfacing layer of SA508Gr.3Cl.2 low alloy steel plate as an example, the effects of the welding specimen machining on the ferrite number measurement results in the stainless steel surfacing layer were studied. By comparing the ferrite number measured by the magnetic method and the chemical method, suitable welding specimen preparation method and ferrite number measurement method were found. The results show that saw cutting and other mechanical machining methods should not be performed when measuring ferrite number by means of the magnetic method. The measured surface should be rasped flat and along the longitudinal direction of weld without staggered processing. Welding specimen machining had no significant effect on ferrite number measurement results when using the chemical method.