Er3+,Tm3+-codoped NaY(WO4)2 crystal was prepared by using Czochralski (CZ) pulling method. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Such optical parameters as intensity parameters, spontaneous emission probabilities, branch ratios and lifetimes are calculated from absorption spectra with Judd-Ofelt theory. Transition processes of the energy levels of Er3+, Tm3+ are analyzed in details and the cross-relaxations: 1G4(Tm3+) + 4I15/2(Er3+)→3F2(Tm3+) + 4I13/2(Er3+), 1G4(Tm3+) + 4I15/2(Er3+)→3F4(Tm3+) + 4F9/2(Er3+) and 3H4(Tm3+) + 4I9/2(Er3+)→3F4(Tm3+) + 4S3/2(Er3+) or 2H11/2 between the two ions are put forward. Through the experiments, we have found that, in this crystal, Tm3+ strengthens luminescence of Er3+ in the green and red regions evidently. The above energy transfer processes provide potential applications of Tm3+ in Er3+-doped laser materials.