MS SQL server query optimizer[1] is an opimization tools that based on a cost model, the database metadata, database statistics, system resources(memory, IO, CPU) and the query itself. if we want to optimize the query in MS SQL server, we must optimize the factor that MS SQL server query optimer rely on. three of that factor is cost model, statistics and the query itself. in SQL Server 2005[2] one tools that can do optimization based on statistic and query is known as DTA. these paper will explain how the query optimizer work, then it will explain how the DTA work side by side with query optimizer and it will explain how to use the DTA to outo optimize the query.