Simulation of thermal desorption spectroscopy (TDS) of the hydrogen isotope-deuterium in tungsten has been investigated in this paper based on rate theory. Data are obtained using polycrystalline tungsten, which is under the irradiation of a plasma with an energy of 40 eV and a dose of 1× 1026 D/m2 at 520 K. By adjusting the trapping energy, trapping rate, and other parameters in the rate theory, we can obtain the TDS simulation spectrum, which coincides with the experimental results. It is found that there mainly exist three trapping states for deuterium in tungsten, whose trapping energies are 1.14, 1.40 and 1.70 eV, and the temperature peaks of them is 500, 600 and 730 K, respectively. These three trapping energies correspond to the energy for trapping the 3rd-5th hydrogen by vacancy (the zero point energy correction has been taken into account), the energy for trapping the 1st-2nd hydrogen by vacancy, and the energy for trapping the hydrogen by vacancy cluster, obtained from first-principle calculation, respectively. It is suggested that the vacancy and vacancy cluster are the main trapping objects for deuterium in tungsten, under the experimental condition mentioned above.