The differences among traditional GIS data models result in difficulty of spatial data integrating and sharing.Commercial GIS vendors and third parties suggested the data conversion solutions.These methods cannot solve the problem perfectly.Geography Markup Language（GML） established by OGC provides standard and framework for spatial data modeling

integrating and sharing.GML has become the defacto international standard for spatial data encoding

transmitting

storing and distributing;more and more spatial data has been stored in GML format.The issue of how to manage the spatial data in GML format efficiently has become the hot one in GIS research.Combining XML database technology and traditional spatial database technology

this paper conducts a deep research on querying and indexing GML data.The spatial extensions to XQuery are suggested.Consequently one GML query language based on XQuery is developed

and native query over GML data is realized.By integrating XML document encoding techniques and traditional spatial index methods

one unified indexing model based on spatial index for GML data is suggested.Taking R-Tree as an example

the performance of the unified indexing model is tested and analyzed through a set of experiments. Experimental results show that the unified indexing model is feasible and efficient.