Abstract: The impact of power grid investment on line loss rate lacks quantitative analysis. Traditional evaluation of loss reduction in transformer areas does not fully consider the transformer losses and loss transfer between transformer areas. This paper, based on the method of synchronous line loss and theoretical line loss, calculates the line loss and transformer loss of transformer areas in a bundled manner, evaluates the changes in the comprehensive line loss rate before and after the addition of transformer areas, quantifies the effectiveness of technical loss reduction, and provides a reference for loss reduction potential analysis and line loss rate prediction.