Abstract: Research on Tm^3＋-doped lasers has attracted many interests since the Tm^3＋ ions have plenty energy levels. The author noticed that the literature is largely confused concerning the designation of energy levels for Tm^3＋ ions. The reason for this confusion is presented firstly by illustrating some examples, and then the spectral terms of equivalent electrons＇system in L -S coupling are calculated for Tm^3＋ ions. At last, a suggestion is given that consistency of atomic states for Tm^3＋ ions should be hold.

Key words: thulium ion, energy level, spectral term, equivalent electrons