Steam power system (SPS) is amajor source of both energy consumption and pollutants. In order to reduce the operational costs for petrochemical industry, the SPS should be operated under an optimal scheme. A SPS model is proposed to take into account the depreciation of equipments, changeover costs, and environmental costs. By applying an improved particle swarm optimisation (PSO) algorithm, the optimal operation scheme has been obtained. One example has been investigated to compare the different units and fuel selection in SPS and also the operation periods of SPS taking in account the power import/export policy and environmental cost.