The invention relates to an ultra-deep hydrodesulfuration catalyst carrier for poor diesel fuel as well as a preparation method and application of the catalyst carrier. The catalyst comprises the following components by mass percent: 2-30% of Ga-modified Y molecule sieve and the balance of alumina, totaling 100%, wherein the Ga-modified Y molecule sieve comprises 0.5-5% of metal Ga; and the amount of metal Ga is calculated by Ga2O3. The catalyst prepared by using the catalyst carrier is applicable to the hydrotreatment process of petroleum fraction oil, particularly the ultra-deep hydrodesulfuration process of the poor diesel fuel.