关键词: 多级安全性（MLS）, 安全模型, 动态安全级

Abstract: This paper gives a multilevel security model based on dynamic security level named Dynamic Multilevel Security（DMLS） model.DMLS uses a couple of dynamic security levels of highest inflow and lowest outflow to replace the current security level of BLP model.With these dynamic security levels，DMLS can control the access of subjects to objects flexibly.In order to use the dynamic security level，DMLS makes a corresponding changes to the five of eleven rules of classic BLP model and the model is proved to be correct through formal methods.At last an application of DMLS to enhance security of linux is given.

Key words: Multi-Level Security（MLS）, security model, dynamic security level