This study reports an investigation on the effects of nanobuds and heat welded nanobuds chains (C60 chains attached or embedded on the surface of a SWCNT) on the mechanical properties of carbon nanotubes by molecular dynamics (MD) simulations. The bond order change and the stress concentration in the distorted connection area of nanobuds when C60 attaches to the surface of the SWCNT are first studied. Then the effect of multiple randomly scattered and attached C60 fullerenes on the ultimate tensile strength of SWCNT is discussed. It is found that both nanobuds and heat welded nanobuds chains lower the ultimate tensile strength of individual defect-free SWCNT. However, the mean post-peak strength of the CNT (after necking) is significantly enhanced by heat welded nanobuds chains. Moreover, the ultimate tensile strength of the SWCNT with vacancy defects does not decrease by heat welded nanobuds chains; interestingly, the maximum tensile strength of the SWCNTs bundles with intertube bridging and vacancy defects even can be enhanced by more than 20% by heat welded nanobuds chains.