To alleviate the poor sensing performance of BiVO, developing new strategies for the fabrication of unique device with improved sensing properties is very necessary and has great practical significance. In this work, size-tailored and uniform black BiVO colloids with abundant oxygen vacancy were synthesized by a unique method of pulsed laser irradiation of colloidal nanoparticles (PLICN). The corresponding laser irradiation effects on the sensing properties are comparatively investigated. The results indicate that the BiVO nanospheres with average size of 50 nm shows best sensing properties with high sensitivity, superior selectivity, low detection limit (44 ppb) to HS at low working temperature (75 °C). Its sensing response is over 4 times higher when comparing with that of the raw material. Further investigation manifests that laser irradiation could induce quantity of the oxygen vacancy and decrease the resistance of the sensing device, which is mainly responsible for the enhanced sensing performance. Moreover, the density functional theories (DFT) calculations suggest that the oxygen vacancies can greatly decrease the surface absorption energy with enhanced HS absorption capability on BiVO surface and lower the bader charger transfer from the absorbed HS molecules to the BiVO, thus enabling the implementation for the enhanced gas-sensing properties.