The integrity noninterference model was investigated based on Rushby’s work.It was shown that the view-partitioned system and the reference monitor assumption-based system defined by Rushby still satisfy noninterfer-ence in the integrity condition as they do in the confidentiality condition;the integrity-noninterference explanation of the Biba model was given;the action-equivalence relation was proposed to deal with the integrity downgrading;two auto-matons

named the equivalent automaton and the purified equivalent automaton

were proposed to aid the noninterference deduction.