Amid the rapid development of the new energy vehicle industry, the vehicle frame, as the core load-bearing component of the entire vehicle, plays a direct role in the vehicle’s safety, lightweight design, and power performance through its design and performance. Although research on new energy vehicle frames has matured, issues related to the lightweighting of drive shaft-associated structures and the balance between weight reduction and strength/stiffness still require in-depth exploration. This study focuses on the chassis of new energy vehicles, utilizing Q295 low-alloy high-strength steel. Based on the vehicle’s dimensions and mass parameters, a simplified 3D model was constructed using SolidWorks. Static analysis under bending and torsion conditions, along with a 6th-order modal analysis, was conducted using ANSYS software. Based on the analysis results, optimizations were implemented at both structural and material levels: structurally, the central crossbeam was widened, holes were opened on the crossbeam’s vertical plane to reduce weight, and the longitudinal beam welding process was optimized; materially, Q295 steel was retained in high-stress zones, while aluminum alloy replaced it in low-stress zones. The optimized frame achieved a 15% reduction in torsional stress, a 16% decrease in bending stress, a 2% reduction in torsional deformation, and a 3% decrease in bending deformation. Total mass decreased by 12.7 kg, with both strength and stiffness meeting design requirements. This approach synergistically enhances frame lightweighting and performance, providing technical support for optimizing the overall performance of new energy vehicles.