Metal chalcogenide solid solution, especially ZnCdS, has been intensively investigated in photocatalytic H₂ generation due to their cost-effective synthetic procedure and adjustable band structures. In this work, we report on the defect engineering of ZnCdS with surface disorder layer by simple room temperature Li-ethylenediamine (Li-EDA) treatment. Experimental results confirm the formation of unusual Zn and S dual vacancies, where rich S vacancies (V_S) served as electron trapping sites, meanwhile Zn vacancies (V_Zn) served as hole trapping sites. The refined structure significantly facilitates the photo charge carrier transfer and improves photocatalytic properties of ZnCdS. The disordered ZnCdS shows a highest photocatalytic H₂ production rate of 33.6 mmol·g⁻¹·h⁻¹ under visible light with superior photocatalytic stabilities, which is 7.3 times higher than pristine ZnCdS and 7 times of Pt (1 wt.%) loaded ZnCdS.