The invention belongs to the technical field of integrated circuit manufacture, and particularly relates to a method for preparing a low-dielectric-constant composite film with nanometer holes. tetraethoxysilane and dipentene serve as precursors, the technology that chemical vapor deposition is enhanced through plasma is adopted, technological parameters such as substrate temperature, radio-frequency power, working pressure intensity in a reaction chamber and the precursor ratio are controlled in the deposition process, an inorganic-organic composite film is obtained through deposition; proper thermal annealing is conducted on the inorganic-organic composite film, so that parts of organic components are thermally decomposed, and the low-dielectric-constant composite film with the nanometer holes is obtained. The dielectric constant of the film ranges from 2.5 to 2.9, under 1 MV/cm field strength, the leakage current density ranges from 10<-8> A/cm<2> to 10<-9> A/cm <2> at the order of magnitude, breakdown field strength is larger than 2 MV/cm, and the mechanical property is excellent. The method is easy to operate and completely compatible with an existing integrated circuit rear-end interconnection technology and is an ideal candidate of an interconnection medium.