Abstract: Mg:Fe:LiNbO₃ crystal sampls were prepared by melt-pulling method.Sample 1^# was reduced in Li₂CO₃ powders at 500oC for 24 h and sample 2^# was oxidized in Nb₂O₅ powders at 1000oCfor 20 h.The inclusion contents of MgOand Fe₂Os are 5 mol% and 0.08 mol% respectively.The absorption spectra of Mg:Fe:LiNbO₃, Fe:LiNbO₃ and Mg:LiNbO₃ crystals and the infrared transmission spectra of Mg:Fe:LiNbO₃ crystal were measured.There is an absorption peak at 480 nm in Mg:Fe:LiNbO₃ crystal, it is responed to Fe²⁺ absorption.There are two absorption peaks which lie at 500 nm and 1200 nm in Mg t LiNbO₃ crystal, they are responed to oxide vacancy Fcenter (V₀²⁺ + 2e^-) and Mg⁺ absorption, but the two absorption peaks in Mg:Fe:LiNbO₃ crystal are very weak and even vanish, this is due to that after Fe ions entered the crystal, Fe³⁺ will trap the electrons which are excited by treating the samples at high temperature and reduced condition, the electrons can't combine with oxide vacancy V₀²⁺ and Mg²⁺ to produce Fcenter and Mg⁺, The infrared transmission spectra of sample 1# show two OH^- absorption peaks at 2.83 μm and 2.85 μm, the absorption peak at 2.83 μm is stronger than that at 2.85 μm, the absorption peak at 2.83 μm is responed to the effect of Mg²⁺ on OH^- lonely, the absorption peak at 2.85 μm is responsed to the effect of Fe ions replacing Nb⁵⁺ on OH^- lonely or to the joint effect of Fe ions replacing Nb⁵⁺, and Mg²⁺ replacing Li⁺ on OH^-, consequently make the OH^- absorption red shift.It is concluded that Fe ions make the resistance of photorefraction decrease, but Mg ions make it increase.The joint effect of the two kinds of ions decides the photorefraction of the crystal.