A super carbon nanotube (ST) is a kind of hierarchical structure constructed from carbon nanotubes (named as CNT arm tubes). With the detailed construction of a Y-junction considered, the effective mechanical properties of ST structures are studied by the molecular structure mechanics (MSM) method. The Young's modulus and shear modulus of STs are found to depend mainly on the aspect ratio of CNT arm tubes instead of the chirality of the ST. A scale law is adopted to express the relation between the effective modulus (Young's modulus or shear modulus) and the aspect ratio of the CNT arm tubes. The Poisson's ratio of the ST is affected by both the aspect ratio of the CNT arm tubes and the chirality of the ST. The deformation of the ST comes from both the bending and the stretching of the CNT arm tubes. The Y-junction acts as an reinforcement phase to make the bending and stretching couple together and induce large linearity in ST structures.