The water level of boiler drum is one of the crucial control parameters for sugar factory. They supply the required steam for heating sugar cane syrup and power generation. To achieve this desired operation, the boilers need to limit water drum level. But, the control of drum water level in boiler is a challenging task. This is because of a specific phenomenon of swell and shrinks that makes difficult to control water drum level optimally. To tackle this problem, various researchers have proposed linear and nonlinear controllers such as solution searching and searching range sharing adjustment of PID, sliding mode controller, Adaptive Neuro-Fuzzy inference system, Fractional Order Proportional Integral Derivative, etc., However, all these controllers lack robustness ,performance and are unable to tolerate steam and water flow rate disturbances. Hence in this thesis, a robust H-infinity-based optimal controller is designed. This controller is robust and has good performance. It also provides high disturbance rejection, guaranteeing high stability for any operating condition.The matlab function augw is used to generate the argumented plant matrix .The matlab script ‘hin f syn 0 synthesized a controller which shapes the signal in order to achieve the required performance and robustness.This controller can be done only by selecting proper weight functions.The weights function W1 is designed as low pas filter in order to achieve small magnitudes of the sensitivity function at low frequencies that ensures good disturbance rejection characteristics and W3 is designed as high pas filter. The coefficients of weight are optimized by PSO. This technique has been selected for the optimization coefficients of weights. To synthesis mixed sensitivity H-infinity controller, the Matlab software with the Robust Control Toolbox has been used. From the simulation result h infinity-based optimal controller is compared with PID and LQR. H infinity controller shows that it has good reference tracking and performance than optimal control LQR and classical controller PID . Keywords: boiler drum, H1 , LQR, proportional integral derivative (PID), optimal control PSO, and turbine