In the environment of body area network ,traditional access control models face challenges such as single points of failure, rigid permissions, and difficulties in dynamic authorization. To address these challenges,this paper proposes a blockchain-based trust-delegation dynamic access control model for BAN .In order to effectively reduce storage and computational overhead, a lightweight two-layer blockchain architecture which separate the management of global policies on the main chain from the processing of specific business on the subchain is designed in the model. A access control logic using multiple smart contracts is builded to enable automated management and execution of delegated authorization. And to enable dynamic permission adjustments, a mechanism for dynamic trust assessment that integrates identity credibility, behavioral history, and real-time physiological context is proposed Through experimental analysis, the model can significantly reduce delays of permission verification and emergency access, improve the success rate of delegation operations, and effectively reduce storage overhead. Finally, it provides a secure, efficient, and flexible access control support for resource-constrained body area network environments.