In this work, a polar molecule 4-mercaptobenzoic acid (4-MBA) is anchored on the surface of CdWO4 by forming Cd-S and W-S bond. Photocatalytic hydrogen evolution is significantly enhanced (about 3.41 times) after the modification. The reason is due to the modification of 4-MBA, which results in a polar surface and built-in electric field. The polar surface is confirmed by the steady state and time-resolved PL spectra, V-oc and SHG results. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.