FeNbSb-related compounds are a group of promising thermoelectric materials. Suppressing the lattice thermal conductivity through different phonon scattering mechanisms could enhance the thermoelectric performance. Previous studies based on the physical transport measurements, it is found that electron-phonon coupling and point defects may play important roles in the suppression of thermal conductivity in FeNb1-xTxSb (T = Zr, Ta and Hf) compounds. In this proposal, we would like to using the inelastic neutron scattering technique to measure the phonon density of states (DOS) in these samples. The comparison of phonon DOSs between these sample, combined with the DFT calculation, could shed light on the phonon scattering mechanisms in these samples.