Copper tungstate (CuWO4) is a promising photoanode for photoelectrochemical (PEC) water splitting due to its appropriate energy band position and broad light absorption range. However, the inherent unfilled 3d atomic orbital of Cu acts as a natural electron-hole recombination site, significantly constraining the PEC performance of CuWO4. Herein, Cs atoms with complete atomic orbitals are doped into CuWO4 in order to obtain better bulk charge separation capability. As a result, the photocurrent of Cs@CuWO4 increases from 0.57 to 0.99 mA cm−2 compared to CuWO4 at 1.23 V vs. reversible hydrogen electrode (RHE) under AM 1.5G illumination, as well as the bulk charge transfer efficiencies rising from 13.5% to 19.3%. In addition, density of states (DOS) calculations further prove that the introduction of Cs atoms effectively suppresses the contribution of Cu 3d orbitals at the Fermi level. This work offers a valuable reference for the advancement of CuWO4 as the next-generation PEC photoanode material.