An introduction is made to the design, development, and core technology of an expressway weather forecasting and service system based on GIS, taking Shaanxi Province as an example. The system adopts the SQL Server 2000 management system database, developed by VB, ADO technology and MapObjects Active technology, which makes the weather query, webpublishing and other GISbased functions realizable and enhances the capability of expressway weather service greatly. Meanwhile, the system has a good portability and can be applied easily in other provinces.