This paper presents a Multi-band Power System Stabilizer Model for power flow optimization in order to improve power system stability. Power System Stabilizer (PSS) is equipment that can be used to enhance the damping of power system during low frequency oscillations. For large scale power systems comprising of many interconnected machines, the PSS parameter tuning is a complex exercise due to the presence of several poorly damped modes of oscillation. The problem is further being complicated by continuous varied in power system operating conditions. In the simultaneous tuning approach, exhaustive computational tools are required to obtain optimum parameter settings for the PSS, while in the case of sequential tuning, although the computational load is fewer, evaluating the tuning sequence is an additional requirement. There is a further problem of eigenvalue drift. This paper presents the multi-band PSS model for designing robust power system stabilizers for a multi machine system. Simulations were carried out using several fault tests at transmission line on a Two-Area Multi-machine Power System. As a reference the PSS model, Delta w PSS and Delta Pa PSS has been used for comparison with the PSS under considerations. The result shows that power transfer response using the model is more robust than Delta w PSS and Delta Pa PSS, especially for three phase faults and phase to ground faults.