The invention discloses a composite desalting, protecting agent material for a masonry cultural relic and a preparing method and application thereof. The composite desalting, protecting agent material comprises a component A and a component B. The component A is a desalting agent and formed by mixing hexametaphosphate and water. The component B is a protecting agent agent and formed by mixing dodecyltrimethoxysilane and ethyl alcohol. Hexametaphosphate and the water are stirred uniformly at the temperature of 20 DEG C-50 DEG C to obtain the component A. Dodecyltrimethoxysilane and ethyl alcohol are stirred uniformly at the temperature of 50 DEG C-70 DEG C to obtain the component B. The application of the composite desalting, protecting agent material comprises the steps of pasting and desalting, wherein water-absorbing paper steeped with the component A is pasted on the outer surface of the masonry cultural relic for desalting; protecting agent, wherein the outer surface of the masonry cultural relic is coated with the component B so that protecting agent layers can be formed. The material is reasonable in design, convenient to obtain and good in use effect, and the masonry cultural relic can be desalted, sealed and protected, and can be protected easily and effectively.