Abstract: According to GB/T 3953-2009 and GB/T 4909.3-2009, multi-group tensile tests and uncertainty assessment were carried out on the electrical round copper wires with initial gauge length of 200 mm and 250 mm respectively. The results show that the percentage elongation after fracture of samples with short gauge length was larger than that of samples with long gauge length, and there was little difference in tensile strength. Standard extension uncertainty of elongation after fracture and tensile strength of two kinds of samples were virtually identical. It is recommended to use short gauge specimen in tensile test.