Currently, the popular DBMS products, for example Oracle、SQL Server、DB2、OpenBASE etc, offer highly efficient query function and complicated optimizing process. However in some circumstances, these successful DBMS query optimizer can not always make an optimal execution plan, even interfere performance. It is necessary to introduce the query hints as an query optimizing auxiliary measure. This paper analyzes the motivation and merit of the query hints, and the effection on the performance, finally describes the hints implementation in the OpenBASE