The invention relates to a grading calculation method for load transfer capability of a power distribution network. The method comprises the following steps: identifying tie lines, buses and power supply stations in an electrical structure schematic diagram; identifying branch lines in each tie line, wherein nodes formed by the branch lines and the tie lines divide the tie lines into a plurality of sections; identifying the minimum element of each section of the tie lines, wherein the constraint condition of the load transfer quantity of each section of the tie lines is the smaller value of the current-carrying capacity allowed by the minimum element, the load transfer quantity of an upper-level line or the power supply capacity margin of an upper-level power supply station; calculating the load transfer capacity of the tie lines section by section, and selecting the tie line with the maximum load transfer capacity as the transfer channel of the bus section; comparing the maximum valueof the load transfer capability with the sum of loads of other non-contact lines of the bus section, and selecting a smaller value as the load transfer capability of the bus; and finally summing theload transfer capacities of the buses to which the power stations belong. The calculation result accuracy is improved, and reliable support is provided for power grid planning and operation mode arrangement.