The invention discloses a calculation method for the line loss rate of a low-voltage transformer area based on a voltage drop method. The method comprises the following steps that A) whether the low-voltage transformer area to be calculated satisfies an archive relation and requirements for the coverage rate and success rate of daily collection is determined; B) data of a master meter and user meters of the low-voltage transformer area to be calculated is collected; C) the single user loss rate corresponding to each user meter in the set collection time within the low-voltage transformer areato be calculated is calculated; D) the loss power DeltaP of all users in the set collection time within low-voltage transformer area to be calculated is calculated; and E) the line loss delta in the set collection time of low-voltage transformer area to be calculated is calculated. The line loss rate of the low voltage transformer area can be calculated accurately without considering practical parameters of low voltage line equipment; and the method provides basis for accurate calculation of the theoretical line loss as well as theoretical support for energy-saving loss-reducing measures.