A recent developed Ni-Cr-Co-Mo-Nb-Ti-Al type nickel-base superalloy, INCONEL 740, has been selected for the application of USC boilers at the temperature above 750°C. This paper focuses on the structure stability improvement of this alloy. Phase computation by Thermo-Calc has been adopted to study main influencing factors on precipitating phases of the alloy and the results show that the ratio of Al/Ti plays an important role. Four new modified alloys in adjustment of Al and Ti contents and in control of Si level were designed and melted for experimental study. The results indicate that the modified alloys exhibit more stable structure stability at 750, 800 and 850°C long time exposure. The newly developed alloy can be adopted for engineering production and application for USC power plants at temperature above 750°C.