The first-principles calculation within density-functional theory is used to investigate the electronic structures and magnetic properties in CuHg2Ti-type alloys FeV2Z (Z = Si, Ge, As, Sb). FeV2Sb is predicted to be half-metal and the energy gap lies in the majority-spin bands. Though FeV2Si, FeV2Ge, and FeV2As show no half-metallicity, their spin polarization of conduction electrons is around 99.7, 99.0, and 97.8%, respectively. The investigation of volume distortion shows that over 99% spin-polarization can be retained in the range of 5.70–6.05 Å for FeV2Si, 5.85–6.05 Å for FeV2Ge, and 5.90–6.00 Å for FeV2As, respectively. FeV2Sb can keep half-metallicity from 6.00 to 6.15 Å. We studied the effects of defects at transition-metal sites and Ge, As, and vacancy substitution for Sb atom on the electronic structures in FeV2Sb, and the results indicate that half-metallicity in FeV2Sb is not sensitive to substitutions for Sb sites.