The invention discloses a synchronous line loss abnormal data identification method based on variable weight rank and approximate equality characteristics in the field of power system line loss data management. The method comprises the steps that a theoretical line loss power data sequence with the same time scale as a synchronous line loss data sequence is solved, and power-electric quantity conversion is carried out; a difference average value of the same-period line loss and the theoretical line loss is sovled, and a difference sequence set is formed; elements in the difference sequence set are ranked according to absolute values by adopting a discrete ranking method; a penalty variable weight method is adopted to assign weights to corresponding ranks of the difference elements, and variable weight positive and negative rank sums are calculated; and a rank sum difference threshold of the abnormal data is solved, and whether the abnormal data exists or not is identified. The methodcan comprehensively consider the influence of abnormal data amplitude and abnormal data quantity, does not depend on index selection for identification, and is high in identification accuracy, strongin adaptability and high in identification speed.