Abstract: To solve the inconvenience or restricted problem of three formulas in GB/T 228.1-2010 to calculate cross-section areas of longitudinal arc specimens cutting from the circular tubes, an uniform formula was established by mathematical deducing method, and that is S0 =0.017 44 a(D－a)·arcsinbD－a. The application examples results show that using this formula to calculate the cross-section areas of the circular tube longitudinal arc specimens, not only the calculation is simple, but also the result is accuracy.