The invention discloses a power distribution network modular planning system based on functional blocks. The method comprises the steps of power distribution network hierarchical division, functionalarea classification, formulation of differentiated power distribution network modularization, formulation of differentiated load density indexes, establishment of a modular power supply model based ontransverse cooperation and longitudinal support, construction of a target network frame planning model, power distribution network structure transition in the middle year and formulation of a hierarchical division guidance principle and a standard system. The beneficial effects of the invention are that: in order to overcome the defect that traditional power distribution network planning is coarse in granularity and solving the problem that existing gridding planning lacks a scientific theoretical system, modular planning requirements of the power distribution network are summaried; on this basis, a power distribution network modular planning system covering four hierarchies of a functional area, a power supply grid, a power supply unit and a functional block is constructed, and a scientific definition and division method of the power distribution network modular planning hierarchy is provided, so that the precision degree of power distribution network planning is improved, and the requirements of society, power enterprises and power consumers are met.