In this paper, H solution behaviors are systematically studied under varied external tensile/compressive strains in bcc W using first-principles calculations. The results show that the H solution energy is not only dependent on the ground state energy of the W lattice, but also strongly dependent on the entropy effect. The entropy effect includes not only the contribution from lattice vibrations, but also the configurational entropy of the H distribution in the interstitial sites. As the entropy effect is directly associated with the temperature, the H solubility in W is strongly dependent on the temperature and the magnitude of the H solubility is increased from 3 × 10-18 at 300 K to 1.1 × 10-3 at 1800 K under strain free conditions. The results also show that external strain can also play an important role in changing the H solution behavior in W. Tensile strain promotes the H solubility while compressive strain suppresses the solution of H.