In body area network (BAN) environments, traditional access control models face challenges such as single points of failure, rigid permission structures, and limited support for dynamic authorization. To address these challenges, this study proposes a blockchain-based dynamic trust delegation access control model for BANs. To effectively reduce storage and computational overhead, a lightweight two-layer blockchain architecture is designed, in which global policy management is maintained on the main chain, while specific service operations are processed on the subchain. In addition, a multi-smart-contract access control framework is developed to enable the automated management and execution of delegated authorization. To support dynamic permission adjustment, a trust evaluation mechanism integrating identity credibility, behavioral history, and real-time physiological context is further introduced. Experimental results show that the proposed model significantly reduces permission verification delay and emergency access latency, improve the success rate of delegation operations, and effectively reduce storage overhead. Overall, the model provides secure, efficient, and flexible access control support for resource-constrained body area network environments.