Abstract-A 471,000kVA Inner-Cooled Turbine Generators, 23kV, .85PF, 3 phases, 50 hertz, 3000 rpm with manufacturing year in 1987, the generator has the service life at over 25 years. The insulation is assumed that is not in an acceptable condition for long term operation and therefore arranges to be performing Life Extension program which will comprise of a full Rewinding of Generator Stator and Generator Rotor. A design margin of the generator should be increased to 494,550 kVA from the current design margin of 471,000 kVA, while maintaining the 0.85 power factor. As justification for the Life Extension program, it will require of life assessment. Then a design review of the generator due to increase a design margin needs to be done by determining the performance and life extension of the generator prior to refurbish or uprating. A design review and feasibility study in order to extend the operating life and increase the capability and reability of the generator are performed by using numerical simulation on magnetic analysis, thermal analysis and rotor dynamic analysis. Therefore, the increasing a design margin on the generators from the current design of the margin will not pose a problem as long as all of the following recommendations can be implemented.