It is encountered in one 135 MW thermal power plant that, during the start-up processes, the desired quality standard for condensed water, feed water and deoxygenated water can hardly be met satisfactorily. In order to prevent the corrosion of boiler and related pipelines, this work firstly introduces and analyzes the corrosion mechanism and the hazards resulting from substandard water quality. The causes of above mentioned problems are then summarized, and solution measures that can be performed in field are also proposed. Finally, the effectiveness of these measures is illustrated through comparing the statistical data.