With the strategic expansion of low-altitude economies, there is a growing demand for unmanned aerial vehicles (UAVs) with enhanced structural reliability and performance. This study investigates the integrated design and precision manufacturing of a heavy-lift quadrotor UAV, focusing on developing a system capable of sustaining substantial payloads. The UAV features an innovative locking mechanism at the base of its arms, which facilitates easy disassembly—this design simplifies maintenance while improving operational flexibility. Structural integrity was evaluated using the Static Structural module in Ansys Workbench under three operational conditions: no-load, full-load, and extreme-load. Results demonstrate that the airframe meets strength requirements under all conditions, though localized nonlinear deformations were observed in the arms under extreme loads. In response to these findings, the Response Surface Optimization methodology was systematically applied to refine the UAV arm’s design parameters, with the dual goals of minimizing structural mass and reducing displacement. Experimental results show that under the most demanding operating condition, the maximum displacement was reduced by 43.6% compared to the pre-optimization state, while the arm’s weight was reduced by 20.2%. These findings provide critical insights for advancing UAV design, particularly in agricultural and logistics applications that require high payload capacity and robustness.