A scheme, which uses flexible key management upon time-token constraint for a user hierarchy access control (UHAC) scheme, is proposed in this paper. For adapting the changeability in a UHAC system, we propose a technique of assigning independent time-token which is distributed by a trusted agency server to reply an authorized user for once secure ac-cess request. The key feature of the technique is to adapt some secure parameters in distributed time-token for responding to each legal access request. Further, all class keys will be updated proactively by the concept of proactive key management, which makes the advan-tage that is proven and free from the scenario of the collusive attack example which proposed by Yi et al. in [14].