Abstract: According to JJF 1059-1999,every factor of S355J2+N steel plate had been tested. Calculating the effects of different factors such as equipment,measuring tool,operator,rounding of numberical values,and the uncertainty of testing was also analyzed,the result of the relative measurement uncertainty was Urel(ReL)=0.9%,Urel(Rm)=0.9%,Urel(A)=0.4%. It was shown that the tensile test procedures were under control normally.