The synergistic catalytic mechanism of anion, cation ions in TiF3, TiCl3 catalysts for LiBH4 has been studied by first-principles method based on density functional theory. According to the results, Ti metal doping in LiBH4 is not easy realized with respect to halogen elements. Co-doping with transition metal and elements in halogen family is achieved easier than doping with Ti alone. For TiF3 catalyst, to achieve doping with one kind of element is helpful to doping with another kind of element, which accordingly results in the increase of doping concentration. Based on the analysis of the electronic structure, we find that doping with halogen element alone can reduce the stability of LiBH4; while doping with Ti alone leads to the rise of Fermi level; the introduction of defect energy level and the weakening of B-H bond; these may be responsible for improving greatly the desorption kinetics of LiBH4 by titanium halide catalysts. The improvement of the dehydrogenating kinetics of LiBH4 with titanium halide catalyst additives is mainly due to the B-H bond weakening, which makes H atom diffuse easily. For TiF3, TiCl3 catalysts, in the reversible desorption process of LiBH4, F and Ti have synergistic action for the B-H bond weakening, but the synergistic action of Cl and Ti is not obvious, this may be the reason for the advantage of TiF3 over TiCl3 in LiBH4 catalytic reaction.