The recent research results about the photo-fragment excitation (PHOFEX) spectrum and the dissociation dynamics of the triatomic molecular ions (CS₂⁺, SO₂⁺, N₂O⁺) are reviewed. The parent ions with state selectivity are prepared via resonance-enhanced multi-photon ionization (REMPI) of neutral molecules using a tunable pulsed laser, and then the parent ions are photodissociated with another laser overlapping temporally and spatially with the first laser. The PHOFEX spectrum is obtained by monitoring the variation of fragment ion signal intensity versus dissociation laser wavelength. From the PHOFEX spectrum the spectroscopic and dissociation information of CS₂⁺, SO₂⁺, N₂O⁺ were derived.