Authorization constraint is an important part in role-based access control models. There are some methods to specify constraint formally, but they mainly focus on the static character. A formal model is proposed to describe time character of constraint in this paper. A founded constraint model, namely a constraint specification language, is studied in detail, and is extended. The language is called RCLT (role-based constraints language with time-character) after extending. At the same time, the problems of optimizing the efficiency RCLT system and restoring to the safe when rules are violated are discussed.RCLT is testified to be able to express the time chracter of constraint well.However,there are further works to be done for finding practical,efficient and general algorithms for optimizing efficiency efficiency and the restoration of safe state,which is the main goal of future research.