The invention discloses a method for calculating a loss benchmark of a regional distribution network. The method comprises the steps of building an objective function aiming at the minimum annual cost per unit area of a power utilization region by taking the power supply radius of distribution lines at all levels as an optimization variable according to the number of outgoing lines of substation at all levels, the number of substations at all levels, the capacity of the substation at all levels and the total length of lines at all levels, then optimizing by using the objective function to acquire the power supply radius of the distribution lines at all levels, then determining a basic value of the loss benchmark value by using the power supply radius of the distribution lines at all levels and standard values of distribution parameters of the distribution network, finally determining a corrected value of the loss benchmark by using a correction model and distribution network parameters in running of a power grid, and correcting the basic value by using the corrected value of the loss benchmark so as to acquire a final loss benchmark value. According to the method disclosed by the invention, the accurate loss benchmark value is acquired by using the optimized power supply radius and different parameters in running, and different accurate loss benchmark values can be acquired for six types of load density regions of the distribution network.