Absorption spectra, emission spectra and excitation spectra of Tm3+-doped NaY(WO4)2 crystals have been measured at room temperature. Such parameters as the intensity parameter, oscillation strength, rate of spontaneous emissions, lifetime and integrated emission cross section have been calculated according to Judd-Ofelt theory and absorption spectra. The intensity parameters are Ω2 = 8.67319 × 10-20 cm2, Ω4 = 1.70424 × 10-20 cm2, Ω6 = 1.55845 × 10-20 cm2. When calculating the spontaneous emission lifetimes, we take into account the magnetic dipole transitions. From the measured spectra, the mechanism of transitions has been analyzed in detail and the cross relaxation 1D2 + 3H6 → 1G4 + 3F4 were put forward and verified.