The invention discloses a computing method of the minimum loss rate of distribution transformers of a regional power grid. The computing method is characterized by firstly, equalizing n distribution transformers with different model numbers in the regional power grid into n equivalent distribution transformers with the same model number; then solving parameters of the equivalent distribution transformers, including the rated capacity, the no-load loss and the load loss; then based on an equivalent distribution transformer loss computing model, solving the minimum loss rate of the distributiontransformers of the regional power grid and the power grid load rate corresponding to the minimum loss rate. By means of the computing method of the minimum loss rate of the distribution transformersof the regional power grid, the minimum loss rate of the distribution transformers of the regional power grid and the power grid load rate corresponding to the minimum loss rate can be solved, the method is simple and practical, and a basis can be provided for economical running and power grid planning of the distribution transformers of the regional power grid.