Bell&LaPadula (BLP) model is the ground for the implementation of multilevel security (MLS) in secure operating systems.The key spirit of BLP model is to make decision on subject's request to access objects according to subject's current sensitivity label.This paper discusses a scheme for the dynamic determination of subject's current sensitivity label.First,as the basis of further exploration,the BLP model is briefly described.Then,the scheme in question is constructed based on the BLP model.Finally,the qualifying condition for the scheme is presented and its necessity and correctness are demonstrated.