The low photochemical activity and stability of sulphides photocatalysts still remain a big challenge for the practical application. In this work, a simple post-synthesis method is developed to partially remove zinc in the as-prepared Zn0.3Cd0.7S sample, in which the unique amphiprotic nature of zinc is utilized mainly. Compared with the untreated Zn0.3Cd0.7S sample (ZCS), the treated Zn0.3Cd0.7S sample (V-Zn-ZCS) by alkaline solution has a 4.8 times higher BET surface area and contains more zinc vacancies. Under visible light irradiation (lambda >= 420 nm), the photochemical activity of V-Zn-ZCS is 1.8 times higher than that of ZCS for the degradation of MB. Moreover, compared with ZCS, V-Zn-ZCS shows an improved photostability after three cycles, which is mainly attributed to the decreased VB oxidation potential by zinc vacancies. It is found that the formed zinc vacancy (V-Zn) can not only change the band structure, but also suppresses charge recombination as the hole trap. This post-synthesis strategy is simple and low-cost, which could be extended to the other photocatalysts. This work would contribute to the practical application of sulphides photocatalysts.