The core of the multilevel security policy is to divide information into different security levels, and to adopt different protection measures according to the security level. This policy is widely used in military field and business environment. This paper introduces three information security models based on multilevel security policy Bell-La Padula (BLP) model, Biba model and Clark-Wilson model. It emphatically expounds and compares the characteristics of the three models. At the end of this paper, the author analyzes the development trend of multilevel security models.