Efficient robust control methods are required to keep the boiler-turbine unit performance appropriately. In this paper, a hybrid multivariable robust control strategy including the regulator and observer is designed to improve the performance of an industrial boiler-turbine unit. In the nonlinear model of the process, output variables including the drum pressure, electric power and water level of the drum are controlled at the desired set-points by manipulation of the fuel, steam, and feed-water flow rates. Due to economic and technical reasons and for the estimation of process states, the full-order observer is designed. For disturbance rejection and process stability, a regulator system is used. The performance of the hybrid control system is investigated in the presence of model uncertainties for two cases. For the regulation purpose, the dynamic system of Case I shows a more smooth variation of drum water level. Finally, it is observed that in the presence of model uncertainties, the hybrid control system guarantees the robust stability and performance of the process in estimation and regulation objectives. Implementation of the above proposed control law in its related electronic circuit of the boiler-turbine will be considered as the future stage of the current research.