Stress is the direct cause of surface oxide scale exfoliation to ruin the protection for alloy matrix. Therefore, it is the key to study oxide scale mechanical behaviour for discovering the oxidation resistance of alloys. In this paper, a new kind of experimental method ‘Archimedes curve slice moment technique’ is studied to test in situ the real time oxide scale stress of ferro-based superalloy K273 during all the high-temperature oxidation. By the derived formula, the oxide scale stress $\sigma$ can be calculated precisely only by observing Archimedes curve slice real-time polar radius OC$^{'}$. Having been oxidated for 5 hours at 800°C, the oxide scale stress versus oxidation time is regressed to follow parabola equation strictly. As the oxides grow and the inner new oxides form in scales to press each other, the oxide scale stress is generated. Analysed by SEM, EDS and XRD, the oxide scale is compact composite structure made up of Cr$_{2}$O$_{3}$ and spinel (Fe, Ni, Mn)Cr$_{2}$O$_{4}$. The less oxide scale stress increment brings about the lower oxidation weight gain rate and the better oxidation resistance. Improved by the use of vacuum system, the Archimedes curve slice moment technique is going to test the oxide scale growing and thermal stresses qualitatively and quantitatively in situ all the time at high temperature.