Abstract: Spatial Data Index is a key basic problem under distributed environment.Control points and Quad-tree structure for spatial data are introduced.These control points are hashed into Chord network.Furthermore,a spatial data index mechanism is put forward,which is based on semantic clustering distributed quad-tree,named SDI-CDQT(Spatial Data Index based on Clustering Distributed Quad-Tree).The Quad-Tree Subdivision,Spatial Data Query and semantic clustering are three main sub-algorithms in the SDI-CDQT.Among of them,semantic clustering sub-algorithm is the key algorithm,which is theoretically analyzed and described in detail.The topology structure of network based on this mechanism is optimized.A lot of experiments show that the SDI-CDQT mechanism is feasible and effective.