We present a study of the electronic and thermodynamic properties of Sr2XMoO6 (X=Ge and Si) based on the density-functional theory first-principles calculations. It is found that Sr2GeMoO6 is a half-metallic ferromagnet and Sr2SiMoO6 is a metallic ferromagnet within the local spin density approximation (LSDA). But using a correlated band theory LSDA+U, the results indicate that both compounds are half-metallic ferromagnets with a total spin magnetic moment per formula unit of 2.00 μB. Through the analysis of crystal-field-splitting and spin-splitting, we find that the main magnetic moment contribution comes from the Mo- states and O- states for both compounds. Finally, by using a quasi-harmonic Debye model, the bulk modulus, heat capacity, Debye temperature and the coefficient of thermal expansion have also been obtained in the present work. The present calculations show that Sr2GeMoO6 and Sr2SiMoO6 may be promising materials for future spintronics applications.