Abstract: The original robust average was calculated from the test results of room temperature tensile test for metallic materials and its robust standard deviation was used for correction. Then corrected robust average and robust standard deviation was calculated. The iterative correction stopped until the robust average and robust standard deviation were stabilized. The assigned value of this proficiency testing results was obtained and its uncertainty was calculated from the final robust standard deviation. The results show that the robust average and robust standard deviation of this tensile test results were stabilized after two iterations, which were 799 N·mm-2 and 6.23 N·mm-2 respectively. So the assigned value of this proficiency testing results was 799 N·mm-2 and its standard uncertainty was 0.7 N·mm-2.