The utility model relates to a sag observation tool for a lead in a high and low voltage circuit, and in particular relates to a measuring sag bar. The measuring sag bar comprises a sag bar, wherein a level bar is mounted in the middle of the sag bar, contraction tapes are symmetrically mounted at the two ends of the sag bar, and hooks are connected to the ends of the contraction tapes. The sag bar provided by the utility model is simple in structure, convenient to carry about and use, and very suitable for use by power line construction personnel; the contraction tapes are provided with scale lines, a sag value can be adjusted randomly, and whether the sag of a circuit is qualified can be correctly and fast judged through the measuring sag bar; the sag bar is provided with marking scale lines to facilitate the application as a measuring tool; and the length of the sag bar can be prolonged by connecting expansion links to the two ends of the sag bar so that the application range is wider.