In steam power plants, continuous efforts have been made to increase the temperature and pressure of the main steam to improve power generation efficiency and to reduce carbon emissions. As a result, advanced ultra-supercritical (A-USC) power plants have drawn the attention of many researchers and industries as one of the future power generation systems. As the steam temperature and pressure increases up to 750 °C and 35 MPa, respectively, Ni-based superalloys have to be applied instead of the previously used austenitic alloys in the high temperature part. One of the key parts in A-USC power plant is a seamless tube for a steam turbine boiler, and IN740H is the most promising material to be used here. IN740H is known to have excellent high-temperature mechanical properties and oxidation resistance among wrought Ni-base superalloys. In this study, we tried to derive an optimal composition range that can improve the oxidation resistance and creep properties of IN740H using various techniques such as thermodynamic calculations and artificial neural networks. In order to find out the effect of composition on oxidation resistance, the cyclic oxidation experiments were conducted with 62 alloys derived using the Box-Behnken method with 7 element variables. In the Cr content range of 22-27 wt.%, Cr did not significantly affect the oxidation resistance. Al was shown to slightly increase the oxidation resistance as the content increased up to 2.7 wt.%, and Ti slightly decreased the oxidation resistance as the content increased up to 2.7 wt.%. Among the spinel former (Mn, Fe, and Co), it was found that an increase in Fe content had the greatest effect on a decrease in oxidation resistance. For the effect of composition on creep properties, 17 model alloys were designed based on the thermodynamic calculations. The model alloys were casted, hot rolled, and heat treated. Then, creep properties were compared under the condition of 800°C-245 MPa. Addition of B improved the creep property by the grain boundary strengthening effect, and the increase of Mo also improved the creep property by increasing precipitation.