The electron emission yields from the interaction of slow highly charged ions (SHCI)He2+,O2+and Ne2+ with clean Si surface are measured separately. It is found that electron emission yield γ increases proportionally to projectile kinetic energy EP/MP ranging from 0.75 keV/u to 10.5 keV/u (i.e. 3.8×105 m/s≤vP≤ 1.42×106 m/s), and it is higher for heavy ions (O2+and Ne2+) than for light ion (He2+). For O2+and Ne2+, γ increases with ZP decreasing in our energy range, and it shows quite different from the result for higher projectile kinetic energy. After calculating the stopping power by using TRIM 2006, it is found that the fraction of secondary electrons induced by recoil atoms increases significantly at lower projectile energy, thereby leads to the differences in γ for heavy ions O2+and Ne2+between lower and higher projectile kinetic energy.