This paper presented to design a robust turbo-generator control system using {{{{ { H}_{$infty$ } }}}} control synthesis for improving small-signal stability. Application study of{{{{ { H}_{$infty$ } }}}} control synthesis is more appropriate in this system since a turbo-generator system is usually operated under circumstance of unmeasurable modelling uncertainty and external disturbance. The{{{{ { H}_{$infty$ } }}}} control theory was briefly reviewed for good understanding and the reasonable approach. The design results are simulated for a case study and to check the system performance in comparison with currently operating Lead/Lag filtered PSS performance.