The study of map generalization has continuously kept up with the pace of the development of cartography and geographic information science. Map generalization has experienced the following steps: early geometric measurement of map elements, graphic simplification, map generalization knowledge applying, map generalization quality evaluation, map generalization methods integration and on-the-fly map generalization and map generalization services. Due to the requirements of mobile geographic information services that the usability of maps have to apply 4A services (Anytime, anywhere, anyone, anything), the theories and technical methods of map generalization in mobile environment should be updated. In this paper we discussed the concept, characteristics and system architecture of map generalization in mobile environment. First, in the broader sense we explained the concept of the mobile environment which the map generalization deals with in and then put forward that this environment should at least include four parts such as computing environment, visualizing environment, transmission environment and applying environment and pointed out that map generalization are different with the traditional map generalization in these aspects. Then we elaborated the concept of map generalization in mobile environment from the point of the fundamental problems in map generalization. Based on the mobility of the user, the characteristics of mobile map generalization such as the range, interaction, constraints, efficiency, visualization were analyzed from different aspects such us the happening mechanism, map cognition and map information transmission. Based on the service architecture of OpenGIS and the Client-Server architecture of mobile GIS, we designed the system architecture of map generalization in mobile environment and analyzed the functions of client and server. At last, we put forward the implementing methods of the system. We used PostgreSQL/PostGIS as the spatial database management system, implemented some map generalization algorithms based on JTS in JUMP and realized the mobile map visualization based on GML and SVG. In this paper we took Hunan road business district of Nanjing as the test area and realized the hierarchical building simplification.