The XRD, emission and IR transmission spectra of Li-doped GdTaO4:Eu3+ phosphors were measured. Judd-Ofelt theory was applied, and the intensity parameters omega2 of Eu3+ for optical transition were calculated. The results show that Li+ codoping can enhance the luminescence intensity of GdTaO4:Eu3+. The intensity can be improved up to 1.7 and 1.5 times, respectively, when x = 0.06 and 0.10. The phenomenon results not from the assumption that Li+ codopant can reduce the crystal symmetry of GdTaO4:Eu3+ so as to relax the parity forbidden transition, but from the flux effect of Li+ codopant which can improve the crystallinity of GdTaO4:Eu3+ and suppress the Gd2O3 and Ta2O5 hetero phases. Gd(0.92-x)Li(x)TaO4:Eu0.08(3+) has not only quite a good crystallinity but also less Gd2O3 and Ta2O5 hetero phases when x = 0.06 or 0.10. Therefore, their luminescence intensities can be improved evidently.