The invention discloses a method for preparing a 
noble metal (palladiumpalladium, 
platinum, silver or gold) decorated nanometer ZnS / 
polyaniline composite photocatalyst, belonging to the technical field of chemical preparations. The method is characterized in that the photocatalyst is obtained through depositing the noble metals on the surface of the nanometer ZnS / 
polyaniline composite photocatalyst, and comprises the following steps of: (1) introducing a 
sulfur source by using a compound of 
conductive polymer polyaniline and Zn2+ as a matrix and using a coordination coordination 
conversion method to convert Zn2+ into 
sulfur-enriched nanometer ZnS among polyaniline links to prepare a composite 
system of the 
sulfur-enriched nanometer ZnS / polyaniline; and (2) reacting a 
noble metal ion with excessive S2-in the composite 
system of the sulfur-enriched nanometer ZnS / polyaniline to prepare the 
noble metal decorated nanometer ZnS / 
polyaniline composite photocatalyst by means of 
chemical deposition. The invention has the characteristics of convenient methods and no need of expensive equipment, the prepared catalyst has favorable 
conductivity and stronger 
photocatalysis, and can be applied to the fields of preparing 
methanol by catalyzing and reducing 
carbon oxide, managing environment 
pollution, sterilizing and the like.