UAV Ad Hoc Networks (UAVANETs) have vast application prospects in various fields, such as disaster relief, environmental monitoring, military operations, and cargo transportation. However, due to the inherent characteristics of UAVANETs—such as limited node resources, high network dynamics, vulnerability of wireless links, and low data transmission efficiency—these networks face significant security threats, including data tampering, information forgery, and Distributed Denial of Service (DDoS) attacks. These challenges pose severe difficulties for task management in complex environments. In response, this paper proposes a blockchain-based secure task management scheme for UAV Swarms (B-SUAVM). Firstly, a dual-layer Practical Byzantine Fault Tolerance (D-PBFT) consensus algorithm is introduced to enhance network robustness and resistance to attacks. Secondly, a dual-layer network structure based on blockchain is constructed to ensure data integrity and security. Lastly, a Cross-Regional Subchain Task Management mechanism (CRSTM) is designed to facilitate the continuous execution of tasks by drones over larger areas. Experimental results demonstrate that the proposed scheme significantly improves task management performance in two different application scenarios, showcasing distinct advantages in data security, network stability, and task execution efficiency.