The thermodynamic properties of CaGeO3 perovskite alloy are investigated using the quasi-hormonic Debye model and the first principles calculation based on the density-functional-theory. The ranges of the pressure [0-12GPa] and the temperature [100-900K] are well selected to study this alloy in its orthorhombic structure. The temperature and pressure effects on the unit cell volume, Bulk modulus, heat capacities, Debye temperatures, thermal expansion coefficient and entropy are determined from the non-equilibrium Gibbs functions. The calculated results indicate that the CaGeO3 perovskite alloy exhibit a negative thermal expansion. The high Debye temperature and high Bulk modulus obtained allow classifying our compounds as hard material with the specificity to store the heat. Also the minimum entropy value obtained confirms that our material is highly ordered.