LiOHFeSe is a layered material that has been extensively investigated for its magnetic states and superconductivity. In this work, an isomer of LiOHFeSe containing FeO and LiSeH layers is computationally investigated. The electron correlation, electronic structures, magnetism and optical properties are calculated and analyzed for both bulk and ultrathin heterostructures. The bulk LiSeHFeO has antiferromagnetic (AFM) state as ground state with a band gap of 1.38 eV. When the system turns from AFM to FM and to paramagnetic states, the band gap shows a monotonic decrease to metallic. On the other hand, LiSeHFeO shows different absorption spectra at different magnetic states, especially in long wavelength region. Then, two types of sandwich heterostructures with two LiSeH and one FeO layer or in a reversal are investigated on electronic structures and optical absorptions. Moreover, their behaviors with the presence of electric field are explored, where a semiconductor-metal transition is observed for the heterostructure of two FeO layers and one LiSeH layer with the increased electric field. These findings may draw attentions to these materials so as to promote the experimental synthesis and potential applications of LiSeHFeO in bulk or film.