The compilation of digital geological maps was a course of digitalization of traditional geological maps and the set up of spatial data information bank.The present foundation for digital geological map compilation was MapGIS compiling system, and took it as a platform to digitalize the geographic elements and geological elements.The digital map of 1∶250 000 scaled Nanjing City was accomplished based on MapGIS platform, the author recorded the primitive data, working method, flow sheet into the operation regulations, and analyzed the establishment of map layers and attributive input, quality supervision of the whole process as well as the major geological contents about the concerned map.