This invention discloses method for feeding Hermetia illucens and used as for preparing composite material of puparium, which comprises the following steps: S1, dry Hermetia illucens pupariums and grind them into powdery, S2, adding powdery of Hermetia illucens pupariums into sodium hydroxide aqueous solution, stirring, separating and filtering, S3, adding the pupariums into hydrochloric acid solution, stirring, separating and filtering; S4, placing the pupariums into sodium hydroxide aqueous solution, stirring, separating and filtering; S5, drying the pupariums, and screening out the granular pretreated powder of the Hermetia illucens pupariums. The invention also disclose preparation method of composite material and thin film of Hermetia illucens pupariums and antibacterial and antimildew additive. The method can effectively improve the yield of chitosan in Hermetia illucens pupariums, and the prepared pupariums powder can be used for preparing polymer composite fibers and thin films of the Hermetia illucens pupariums, thus, the antibacterial effect is greatly improved. A new antibacterial and antimycotic additive can be obtained by compounding the powder of Hermetia illucens pupariums with the powder of oyster shell.