We show a structural modification technique which causes the fluctuated surface of multi-wall carbon nanotubes ( MWNTs) by using hydrogen sulfide as a reaction-assist medium, which promotes the formation of sp(3)-hybridized orbitals of carbon and suppresses the formation of sp(2)-hybridized orbitals in the plasma process. We observed the structure of MWNTs synthesized with the addition of H2S by means of high-resolution transmission electron microscopy and electron energy loss spectroscopy, and found the cornhusk-like surface fluctuations on the surface of MWNTs. In this study, we discuss the mechanism underlying this structural modification of carbon nanotubes precisely.