Abstract: The importance and necessity of economic loss assessment of power quality problems is discussed in the paper and the idea of meaningful classification of power quality problems is emphasized. According to the characteristics of continuous power quality problems, all problems are divided into two intervals, namely acceptable and unacceptable, and assessment methods based on quality loss function are proposed to calculate the economic loss caused by the continuous power quality problems in unacceptabe interval. In addition, effects of eventbased power quality problems are fully considered, and their direct and potential economic loss assessment models are determined according to their influence.At last, the idea of selective governance of power quality based on ecomomic loss assessment is proposed, which solves the balance problem between technical and economic efficiency.