This paper proposes a new multi-areaframework for unbalanced active distribution network (ADN) state estimation. Firstly, an innovative three-phase distributed generator (DG) model is presented to take the asymmetric characteristics of DG three-phase outputs into consideration. Then a feasible method to set pseudo -measurements for unmonitored DGs is introduced. The states of DGs, together with the states of alternating current (AC) buses in ADNs, were estimated by using the weighted least squares (WLS) method. After that, the ADN was divided into several independent subareas. Based on the augmented Lagrangian method, this work proposes a fully distributed three-phase state estimator for the multi-area ADN. Finally, from the simulation results on the modi?ed IEEE 123-bus system, the effectiveness and applicability of the proposed methodology have been investigated and discussed.