The invention belongs to the technical field of nano-structured functional films and particularly relates to a silver salt and cerium salt codoped cuprous thiocyanate composite film and preparation and application methods thereof. The silver salt and cerium salt codoped cuprous thiocyanate composite film is prepared by taking cuprous thiocyanate as precursor and soaking the precursor sequentiallyin silver nitrate solution and cerium chloride solution. One of applications of the silver salt and cerium salt codoped cuprous thiocyanate composite film is to serve as the substrate of surface-enhanced Raman spectra to detect trace organic molecules and achieve an extreme detectable concentration as low as 10<-10> mole per liter.