TiMn₂-based alloys hold significant application potential due to their moderate hydrogen storage operating conditions and exceptional volumetric hydrogen storage density. Industrial by-product hydrogen, which is widely available and relatively cheap, often contains components such as H₂S, CO, and CH₄, whose poisoning mechanism on TiMn₂-based alloys in the process of hydrogen absorption and desorption remains to be elucidated. In this work, the poisoning mechanisms of H₂S, CO, and CH₄ on Ti_0.8Zr_0.2Cr_0.75Mn_1.25Ce_0.01 hydrogen storage alloy were investigated by isothermal adsorption curve, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope-energy dispersive spectroscopy (SEM-EDS). The results showed that the toxicity of impurity gases on the alloy is CO > H₂S > CH₄, and the regeneration difficulty was H₂S > CO > CH₄. The hydrogen absorption of the Ti_0.8Zr_0.2Cr_0.75Mn_1.25Ce_0.01 alloy was restored to 58.59% after five groups of H₂S poisoning-regeneration cycles. The hydrogen storage capacity retention rate decreased to 4.03% after five groups of CO poisoning, but the alloy recovered to 96.62% of the hydrogen absorption capacity after regeneration with pure hydrogen. The retention rate of the alloy was 100% after 100 cycles of CH₄ poisoning. According to the results of XPS analysis, two metal sulfides (TiS and ZrS₂) and one metal sulfate Zr(SO4)² were formed after the Ti_0.8Zr_0.2Cr_0.75Mn_1.25Ce_0.01 alloy was poisoned by H₂S. Therefore, H₂S poisoning belongs to irreversible adsorption and CO belongs to reversible adsorption. The poisoning mechanism may guide the design of alloys for the absorption/desorption of industrial by-product hydrogen.