Abstract: The proof total extension strength Rt0.5 is one of the most important mechanical properties of pipeline steels, and it is also necessary to ensure the safe operation of pipelines. Through comparing the tensile test results of X70 pipeline steel samples with different sampling direction and flattening degree, the effects of sample preparation factors on Rt0.5 test results were analyzed. The results show that the measured Rt0.5 of longitudinal direction samples was largest, so sampling direction must be indicated in the product supply agreement. The incomplete flattening of tensile samples would cause Rt0.5 test results fluctuation. In order to guarantee the accuracy of Rt0.5 test results, the tensile samples must be flattened completely before test.