The invention discloses a method for producing a water soluble moistureproof film coating premixing agent, which relates to a pharmaceutical excipient. The premixing agent consists of raw materials, namely polyvinyl alcohol, polyethyleneglycol, hydroxypropyl methylcellulose, castor oil, tween-80, color lake, titanium pigment and talcum. The raw materials are mixed according to certain weight percentage, and the premixing agent is produced according to the prior process for producing the film coating premixing agents. The method has the advantages that the water soluble moistureproof film coating premixing agent produced according to the formula has good film-forming property, firm combination of a coating layer and a medicament core, strict wrapping, uniform thickness and even coloration, is smooth and beautiful, has good moisture resistance and oxygen insulation, can avoid surface abrasion, edge cracking, peeling or adhesion of a finished coating agent product and the like, and can better meet various needs of film coatings of solid pharmaceutical preparations.