Farmland environmental deterioration is the main reason which results in the agricultural product quality problems, so it is necessary to build a geospatial information system for farmland environmental monitoring and management. The rapid development of portable farmland environmental surveying or sampling devices and sensor network have made this possible. In this paper, we describe the design and implement of the geospatial system based on Flex and Web Services. This system provides data management, geoprocessing, visualization, as well as analysis functions to mine potential valuable information to support decision making based on the sampling data and other collected environmental data of farmland. Geoprocessing is implemented by directly invoking Geo-processing Web Services or calling Server APIs. To enhance the usability, the system also provides a flex client for users and web service interfaces for client program. Tertiary user structure with strict privileges management is designed to protect the users’ data copyright.