Au-Cd 1-x Zn x S core-shell nanocrystals (NCs) with controllable shell compositions (from x = 0 to x = 0.37) were synthesized by using the hot-injection method. By increasing the mole fraction of ZnS in the Cd 1-x Zn x S shell, the conduction band of Cd 1-x Zn x S can be cathodically shifted to cause an increase of energy difference between the conduction band level of the Cd 1-x Zn x S shell and the Fermi level of the Au core, thereby enlarging the driving force of interfacial electron transfer to enhance the photoelectrochemical (PEC) efficiency. The interfacial charge dynamics of the samples were examined by time-resolved photoluminescence (TRPL) spectroscopy. The results showed that the interfacial electron transfer rate constant (k et ) from the Cd 1-x Zn x S shell to the Au core was increased by 2 orders of magnitude, from 2.41 × 10 7 to 4.91 × 10 9 s -1 as the mole fraction of ZnS increased from 0 to 0.37. Furthermore, PEC characterization, including Mott-Schottky analysis and photovoltage decay measurements, illustrated that gradually introducing ZnS into the shell composition of Au-Cd 1-x Zn x S NCs can modify the band structure and enhance the effectiveness of interfacial ET for advancing the PEC properties. The practical use of Au-Cd 1-x Zn x S NCs in PEC methanol oxidation was also demonstrated, revealing their promising potential as viable photoelectrodes for various PEC applications. The present study delivers an alternative approach of modulating the interfacial ET dynamics of core-shell MSNs by means of shell composition adjustment. The illustrations provide an empirical guideline to the intelligent design of core-shell metal-semiconductor nanoheterostructures (MSNs) for the desired PEC applications.