Abstract: Conception of secure labels is analyzed, and defined by formalization, subsequently the lattice model theory of labels for dynamic multi-level security is established, which shows that the set of secure labels for dynamic multi-level security comes into being "lattice order" in math, and solves the existence of g.l.b and l.u.b when one secure label compares to other, and establishes the theoretical basis for change from static multi-level security to dynamic multi-level security according to the history sensitivity.