Abstract: Under the circumstance that there are too much isolated nodes in recent DTN routing algorithm that seriously affect the performance of the whole network. This paper proposes a social DTN message transmission strategy based on line graph. The algorithm takes the quality of node pair and similarity in the line graph into consideration,and then divides nodes into different communities within three hops periodically. Finally,different routing strategies are designed in the community and between communities to achieve data transmission. Simulation results show that compared with Epidemic,PROPHET,and Sim Bet algorithm,the algorithm has higher message delivery ratio and smaller network overhead without any increase in network latency.