Abstract: Targeted at the reality of weak technology and limited defense facilities in grassroots department of Guangdong Province,this paper proposes a new model for defensing mountain flood disaster based on“one map and one manual”. Based on GIS mapping theory,through map synthesis methods such as symbol thinning,map representation,and marker dispersion etc. This paper completes making defense maps and defense manuals of mountain flood disaster for 7 cities at county-level and town-level,this would promote the formation of“one map and one manual”mountain flood disaster defense system at the grassroots. At the same time,a WebGIS-based defense atlas information management system is developed,which provides a unified data access and security control mechanism,realizes the functions of visual display,dynamic management,online update and traceability of various data,and helps to ensure the authenticity,accuracy and real-time of data. The results can effectively break through the terminal blockage of information transmission,solve the problem of passive decision-making in the“last mile”,promote the full sharing of data resources for mountain flood disaster defense operations,and strengthen the defense capability of mountain flood disasters at the grassroots level.