Abstract: Deepwater suction pile foundations for subsea wellheads are characterized by large diameters and shallow embedment depths. However, existing design methods mostly draw on suction buckets used in offshore wind turbines, and a structural parameter optimization system tailored to subsea wellhead loads and functional constraints is still lacking. To optimize the combination of suction pile diameter and penetration depth while satisfying the requirements for wellhead stability, centering accuracy, and verticality control, thereby improving installation efficiency and reducing well construction costs, theoretical analysis and laboratory model tests were used to conduct penetration and bearing performance tests on suction piles of multiple specifications. Equal-lateral-area models with diameters of 10−50 cm and corresponding length-to-diameter ratios of 1.2−6.0 were designed. Under different suction flow rates and undrained shear strengths of the soil (20 and 25 kPa), gravity penetration, negative-pressure suction-assisted penetration, and vertical and horizontal bearing capacity tests were completed, and the sensitivity of each parameter to installation characteristics and bearing capacity was analyzed. The test results showed that increasing the model diameter from 10 cm to 50 cm decreased the gravity penetration depth by 58%−62%, and increasing the suction flow rate from 20 L/min to 60 L/min increased the ultimate penetration depth by 35%−45% on average. Under equal-lateral-area conditions, the difference in vertical bearing capacity among different suction pile models was less than 5%, and the horizontal bearing capacity increased by 48.7% as the diameter increased. Based on the test data, a chart for selecting optimal structural dimensions of suction piles under equal vertical bearing capacity conditions was developed, and a structural selection framework satisfying the design indices was established. The research findings can provide theoretical support for the structural optimization and field construction of deepwater suction-pile-based subsea wellheads.