Metal hydrides are promising moderator materials in advanced reactors, where their thermal neutron scattering cross sections significantly affect the accuracy of reactor design. This study uses special quasi random structure (SQS) and first-principles lattice dynamics methods to calculate parameters such as the phonon densities of states of sub-stoichiometric zirconium hydride (ZrH_x) and yttrium hydride (YH_x). Based on these parameters, thermal scattering law (TSL) data for sub-stoichiometric hydrides are generated using the nuclear data processing code NECP-Atlas. The influences of hydrogen content on the thermal scattering cross sections of hydrides and the effective multiplication factor (k_eff) values of critical assemblies are analyzed. The result shows that variations in hydrogen content within hydrides lead to differences in thermal scattering cross sections, consequently affecting the neutron transport calculations of nuclear reactor. For the ICT003 and ICT013 benchmarks loaded with ZrH_x (with H/Zr ≈ 1.6), using the TSL data derived from ZrH_x with other hydrogen content results in a maximum deviation of 104 pcm in k_eff. For the HCM003 benchmarks loaded with ZrH₂, the use of TSL from ZrH_x with other hydrogen content leads to a maximum deviation of 147 pcm in k_eff.