Data sets of point and interval dimensions are important in spatial database system and GIS. This paper proposes an index structure PI-tree for the data sets of point and interval dimensions, based on an analysis of R^*-tree and SS-tree, of which the former is used to demarcade multidimensional space of data set using hyper-sphere with the aim of improving accessing and reducing the I/O times of inserting data. Furthermore, the algorithm of insertion, deletion and retrieval of PI-tree is also presented. Finally, the analysis and results of experiment show that PI-tree outperforms R^*-tree.