The key parts of special electromechanical device landing, expansion and righting mechanism like support plate torsion spring takes the advantages such as large working deformation angle, longevity of energy storage time, small structure size, and prefect stress corrosion relaxation property and so on. According to the job demands, we adopt torsion spring type selection, torque calculation, initial condition definitive, key parameter selection and other parameter calculation; take the study on stress relaxation properties of support plate torsion spring takes, put forward to stress corrosion relaxation property and take Adams for simulation analysis. What we have done prove that this design is reasonable, which can meet the actual needs.