High-precision five-axis machining puts forward strict requirements for the stiffness and position stability of the AC double-angle milling head, especially when the gear transmission system is used under heavy cutting load and complex force coupling conditions. In the actual processing environment, the non-uniform deformation caused by structural coupling and load changes will directly affect the machining accuracy and stability. In order to solve these problems, this paper designs and analyzes a gear-type AC double-angle milling head with a pendulum structure and a layered modular structure. A parametric finite element model was established, and ABAQUS software was used to conduct a static analysis of two typical A-axis directions (0° and 90°), taking into account the internal prestressing force generated by gravity, cutting force, and gear meshing to reflect the typical working conditions. Under the same boundary conditions and load conditions, the influence of different structural materials on the overall stiffness was further studied through comparative analysis. The results show that under the conditions of five-axis linkage machining and positioning machining, the overall deformation of the milling head is maintained within the micron range, which meets the requirements of high-precision machining. The deformation behavior shows obvious dependence on the A-axis direction, reflecting the inherent anisotropic stiffness characteristics of the structure. Compared with the traditional structure, the proposed design has better rigidity performance under combined load conditions and provides practical reference values for the subsequent structural optimization, material selection, and precision control of high-performance five-axis CNC milling heads.