Abstract: Metro is one of the most important public transport systems in modern society.The reliability of connec-tivity is not only affected by uncertain factors (e.g.operational failures,terrorist attacks,and stampedes),but also close-ly related to network structure.To evaluate the impacts of network structure (in terms of different composition of lines) on the reliability of the connectivity of the metro network,the concept of "the importance of line connectivity" and the corresponding models are developed to study the difference (in percentage)before and after line addition/removal based on the theory of the reliability of connectivity.An order-based algorithm integrated with a judgment algorithm is used to find solutions for the proposed models.Metro Network of Guangzhou in 201 5 (i.e.a typical grid network)is selected as a case study to evaluate the impacts of line features (e.g.number of stations)on the reliability of network connectivity.The re-sults show that the Line 3 consistently has the highest connectivity importance (reaching 99.84%).As a key line,its im-portance is jointly affected by the number of transfer stations and intermediate stations.The impact of the former is more significant than the latter.It is suggested that in-depth studies and evaluations should be carried out to prioritize the poli-cies related to metro construction and maintenance .