Power plants unit loading optimization problem is of practical importance in the power industry. It generally involves minimizing the total operating cost subject to satisfy a series of constraints. Minimizing fuel consumption while achieve output demand and maintain emissions within the environmental license limits is a major objective for the loading optimization. This paper presents a Particle Swarm Optimization (PSO) based approach for economically dispatching generation load among different generators based on the units’ performance. Constraints have been handled by a proposed modified PSO algorithm which adopting preserving feasibility and repairing infeasibility strategies. A simulation of an Australia power plant implementing the modified algorithm is reported. The result reveals the capability, effectiveness and efficiency of using evolutionary algorithms such as PSO in solving significant industrial problems in the power industry.