The secure limitation in the database system only taking discretionary access control is discussed. This paper proposes a mandatory access control model for multilevel secure DBMS and discusses the problems of labeling object in tuples, security label, covert channels and poly-instantiation. The mandatory access control model requires that all users and resources are classified and assigned a security label, which is a combination of a hierarchical security level and non-hierarchical security categories. As mandatory access control plays an important role in highly secured database system, the model is analyzed and implemented in independent copyright database management system LogicSQL. In addition, the model is designed at least with a B1 security level for LogicSQL database.