Based on complex network theory， the invulnerability evaluation of typical network structures for the medium voltage distribution networks is proposed. The corresponding nodes and node weights， edges and edge weights， initial weights and other basic concepts are defined. An invulnerability evaluation model for medium voltage distribution networks is proposed for the invulnerability evaluation of weighted networks. The model can be used for invulnerability evaluation with quantitative ordering of typical network structures of medium voltage distribution networks. The method enriches reliability analysis theory of the medium voltage distribution network and provides a new basis and means for the choices of typical network structures for the medium voltage distribution network. Results from case studies confirm the validity of the qualitative assessment of the security of typical networks. The rationality of the method is also clearly shown through the case studies.