With the development of the domestic GIS technology, the geographical information systems are widely used in various domestic industries. The south CASS data format is mainly used in digital surveying and mapping, along with the GIS technology. To reduce the cost of the GIS application system and to improve the GIS system efficiency, the timely updating of the GIS data and the geological and mineral resources is of great significance. The MapGIS software is often used in the geological fields, but the CASS software is often used in digital surveying and mapping, and their data formats are quite different.. In view of practical applications, this paper discusses the formats of the data characteristics and the conversion method between CASS and MapGIS. To read the CASS data, the CASS diagram entity types are subdivided into point, line, surface, text, and block. Then the data are converted to the MapGIS format as dot, line, face, text, and sub graph. In the conversion practice for the Inner Mongolia Baotou Habuqin iron mine topographic map, the automatic conversion of the two kinds of data formats are realized and the data loss is reduced in the process of conversion.