Inefficient heat dissipation in vapor chambers (VCs) is a major challenge for their development and application. To investigate the effect of supports on VCs’ maximum thermal power and thermal resistance, the relationship between the number of supports and the vapor channel pressure drop is studied through pressure drop measurement. Composite Wick Vapor Chambers (CWVCs) with various supports are fabricated and tested with a constructed thermal performance test platform. The results indicate that the heat transfer performance of CWVC is related to the number of supports and the liquid filling ratio. The optimum filling ratio of the composite wick with 3-6 spiral supports (SS3-SS6) is 60%, 70%, 90%, and 70%, with corresponding maximum thermal power of 19.25 W, 25.61 W, 25.97 W, and 21.22 W. The thermal resistance of SS4-CWVC is lower overall. Additionally, when the power is 21 W, the surface temperature difference of the condenser of SS3-CWVC and SS6-CWVC is 2.3 °C and 1.3 °C, respectively. However, the condenser surface temperature difference of SS4-CWVC is 66.5% lower than that of SS3-CWVC and 40.8% lower than that of SS6-CWVC at the same power. Therefore, SS4-CWVC exhibits better temperature uniformity and has better heat transfer performance.