Structure variable Robots are proposed as novel mobile robots based on tensegrity structures. They consist of rigid struts and tensile cables and can generate rolling gaits by self-deformation. Recent designs for tensegrity robots are mostly based on experience, and fixed drive parameters are used in the rolling control. The influence of the diving parameters and material parameters on the performance (such as rollability, energy consumption, and structure reliability) is necessarily but has not been discussed, since the tensegrity structures are highly coupled and the analysis based on the traditional kinetic methods are complex. For obtaining low energy consumption, high rollability and high reliability, the gravitational torque, critical driving length and driving force are used as performance criteria to describe three performances, and then the finite element method is applied to find out the relation between the driving parameters, material parameters and the three performance criteria, and optimal parameters are chosen to obtain better performance. A 6-strut tensegrity robot platform is built and experiments have been taken on this robot to test the validity of the computational results.