This paper analyzes the structural composition of the locking mechanism for electric heavy-duty truck battery swapping and proposes a design method for a hook-type locking mechanism. Aiming at the problem of sensor misreporting of unlocked faults caused by the potential interference between the lock hook and lock block due to manufacturing errors, an innovative clearance fit design for the lock hook and lock block is developed. This design not only ensures battery safety but also improves the stability of the locking mechanism. Verified by simulation analysis and durability tests, the optimized locking mechanism meets performance requirements under vibration, fatigue, and extreme working conditions, which can provide theoretical reference for the design of battery-swapping devices.