To make the designed rover have self-adaptability and better contact with ground, DOFs required for single suspension system and the whole rover are studied. Three classification ways of self-adaptability are given, and the relationship between self-adaptability and climbing performance, stability, energy consumption is analyzed. Mathematic model of single wheel-suspension system is established and such system’s DOF is obtained. Based on aforementioned analysis, mathematic models of double, three and k wheel-suspension system are established respectively with calculated DOFs for these systems. Two DOF models for wheeled rover are given followed by DOF statistics and analysis of some representative self-adaptive rovers. The analysis shows that self-adaptability is the basis for realizing comprehensive performance of the locomotion mechanism. DOFs for single suspension system and rover are 1 and 3, respectively. The conclusion has universalism and can determine required DOFs for structural synthesis of wheeled rover.