Abstract: Spatial 　indexing　seriousl y　impacts 　the 　efficienc y　of 　spatial 　processing．In　this　papera　new spatial 　index　based　on　double 　transformation DT－indexis 　proposed．As 　a　dimensional 　transformation 　the　DT－index　benefits 　from　both　hi gh　and 　low　dimensional　mapping．The 　spatial 　objects 　are 　partitioned 　in 　se quential 　queuemore　efficient 　than　area 　partitioning．A　spatial 　join 　al gorithm　based　on　the DT－index 　is 　introduced 　and　optimized　with　a　quad－tree．The 　experimental 　results 　reveal 　that 　the　proposed　method　improves 　the　performance 　of 　spatial 　join 　processing　in 　terms 　of 　redundanc y　and　speedup ratio 　through　a　comparison　with　the　widel y－used　R－tree　method．