The basal plane of MoS2 possessing the highest specific surface area was always neglected in catalysis due to its inert surface. While in a biaxial strained MoS2, the surface can possibly be activated by creating stable S-vacancies. By analyzing the electronic properties of the S-vacancies, we found that the catalytic activity for CO methanation could be exploited. In view of this aspect, the mechanisms of S-vacancies formation, CO and H-2 adsorption and CO methanation have been investigated through DFT approach. The results indicated that CO methanation on the activated basal plane of MoS2 can be proceeded more easily once it was being activated. The activated basal plane of MoS2 is even more active than the active sites over some specific edge surfaces.