Using the growth rate method, we obtain the single-electron detachment (SED) cross-sections for 5-30keV C-+He, and double-electron detachment (DED) cross-sections for 5-15keV C--+He. The SED cross-sections first increase with the increasing incident ion energy, and then decrease with further increase of the energy. The DED cross-sections increase with the increasing incident energy in the 5-15keV region.