There are many factors affecting the ArcGIS Server system, therein, the map image itself is one of the key factors. In the ArcGIS Server System-the Satellite Remote Sensing Dynamic Monitoring System for Marine Law Enforcement of Yangtze River Valley, map data are optimized by image layer arrangement, optimization of map rendering, field length arrangement, application of map cache mechanism and so on. Therefore, the access speed for maps in the system is increased greatly. In this paper, the methods for map data optimization are introduced in detail and then discussed.