The invention relates to a blue-green silicate long afterglow luminescent material and a preparation method thereof. The chemical expression of the luminescent material is Ba0.9975Si2O5:Eu0.0025, Rx,wherein R is one or two of Dy, Pr, Ce, Nd, Tm, Sm, Yb, Gd, Er, Tb or Ho, and x is more than or equal to 0.005 and less than or equal to 0.050. The preparation method comprises the steps of respectively weighing raw materials according to a stoichiometric ratio, grinding the weighed raw materials, and evenly mixing to obtain raw material powder; carrying out calcination, cooling, and then grindingto obtain the ultra-long blue-green silicate long afterglow luminescent material. According to the preparation method, Eu<2+> is used as activation ions, one or two of trivalent rare earth ions such as Dy<3+> and Nd<3+> are used as co-activation ions, a co-solvent is not added, and calcinations is carried out at low temperature; the luminescent material prepared by the method can emit blue-green ultra-long afterglow after being excited by light with a wavelength of 200-400 nm. The blue-green silicate long afterglow luminescent material has the advantages of being simple, free from pollution, energy-saving and low in cost.