The invention provides a power distribution network state estimation method based on network decomposition. The method comprises the following steps that a power distribution network is decomposed; sub-network state variable initialization is carried out; loop iteration solving is carried out; constraint condition equivalent measuration weight is computed; a sub-network state variable is solved; whether a convergence condition is met is judged, if yes, iteration is completed, and power distribution network state estimation results are output; and otherwise, 1 is added to iteration times automatically, and loop iteration solving is carried out. The applicability of a state estimation algorithm is improved, a large network can be subjected to state estimation, by network decomposition, the data scale of a node admittance matrix is lowered, the storage space requirements and computing complexity are lowered, for the large network, compared with direct computing, computing speed is high, and efficiency is high.