The invention relates to a method for determining a power system parallel load flow based on heuristic automatic network partitioning, which comprises the following steps: partitioning distribution network; generating the admittance matrixes of the partitioning nodes, the power flow calculation constant-jacobian matrix and the voltage-power sensitivity matrixes of virtual generators in partitions, sending the voltage-power sensitivity matrixes to a coordination layer; sending initial voltage magnitude and phase angle of virtual engines at the split points by the coordination layer; carrying out power flow calculation on the partitions, sending output power of the virtual engines to a coordination server; judging whether the boundary coordination quantity precision is met or not according to the mismatch quantity of the sum of output power of two virtual engines at the split points by the coordination layer, if no, correcting the voltage of the partitioning points, sending the corrected result to sub-areas, skipping to the last step, and otherwise, skipping to the next step; outputting the data result. The determining method has good convergence, high calculation speed, less memory occupied rate and calculation convenience and flexibility.