Abstract: According to the method processes of GB/T 228-2002,tensile test was carried on TC4 titanium alloy bar. The mechanical properties of TC4 material,including the yield strength,tensile strength,the length after rupture and the shrinkage of fractured cross-section were measured. Meanwhile,the causes of the metal bar sample tensile testing uncertainty from the following aspects: sample size measuring,testing machines,extensometers,the revision of test data and the material discontinuity and evaluated the uncertainty measurements were analyzed. Conclusion of the testing result was alsodiscussed. It would have a certain reference value to the evaluating of other metal bar material tensile uncertainty.