For the purpose of testing the watermelon’s interior quality nondestructively, the sub-band spectrum centroid of the impact vibration response was employed as the characteristic parameter to describe and model the soluble solid content (SSC) and the flesh color of watermelon. A total of 76 watermelon samples were used in the experiments, for both the nondestructive vibration tests and the destructive SSC and color tests. Different impact methods and positions were attempted to validate the robustness of the sub-band spectrum centroid as a characteristic parameter. The results showed that the sub-band spectrum centroid had low dependency on different impact methods and positions, which could greatly simplify the complexity of the testing system. The optimized sub-bands were obtained for modeling the SSC and the a* value of color with determination coefficients of 0.8124 and 0.7336, respectively, which were higher than that when the resonant frequencies were used as the characteristic parameter. Linear models were made for both SSC and a* value. The vibration subband spectrum centroid was gone down monotonously along with the SSC (sub-band 144~416Hz) and a* (sub-band 148~428Hz) value, with the slope of -1.361 and -1.019, respectively. However, the subband spectrum centroid had low ability of describing the L* and b* values in color testing, whose determination coefficients were only 0.52 and 0.148, respectively.