The measurement results on 200—1000nm excitation spectra of light from a solid surface of Ti which is excited by slow highly-charged ions(SHCI) 126Xeq+ （6≤q≤30）with a kinetic energy of 150keV are reported. The results s how that the characteristic spectral lines of the target atoms can be effectivel y excited by the SHCI even though the beam intensity of the incident ions is ver y weak (only about one per one nanosecond). We have also found that when the num ber of the peeled electrons of the projectile is beyond a critical value which d epends on the properties of the target, about 20 for Ti, the spectral intensity of the characteristic spectral lines can be greatly enhanced. Theoretical analys es show that this phenomenon is closely related to the surface plasmon excitatio n of the free electron gas of the metal surface during the potential energy rele ase of the single-electron transfer when the number of the peeled electrons is b eyond the critical value.