Abstract: As the temperature is a key factor affecting melt glass dissolution rate, the decay heat power generated by radionuclides within melt glass from 10 d to 300 000 d after an underground nuclear test was calculated to assess its influence on temperature and dissolution rate. Radioactive inventories with half-life longer than 1 a, produced by 100 kt TNT nuclear explosion published by IAEA report were used. The inventories of short-lived fission products with half-life of 1 d-1 a and accumulate yield greater than 0.1% were estimated from the inventory of ¹³⁷Cs. The decay characteristics of each nuclide were analyzed. The decay energy deposited in melt glass was calculated by the mean alpha, beta and gamma energy released by radioactive decay from ENDF/B Ⅶ database. From the calculation, it can be concluded that the decay heat power decays by power function, short-lived fission products, long-lived fission products and actinides are the main contributions to the power at 10-2 000 d, 2 000-60 000 d and after 60 000 d, respectively. The influence on melt glass temperature and dissolution rate is indistinctive, especially after 1 000 d.