SiO2 colloidal crystals with silicon spheres diameter of 270 nm were used as templates and MMA was filled in the gap of silica spheres. SiO2/PMMA photonic crystal with a overlayer of PMMA was obtained by polymerization reaction. SiO2/PMMA was immersed in a 20 wt% HF aqueous solution. After etching half an hour, the flexible PMMA film with inverse opal structure peeled off from the TIO glass substrates. The thin film is a kind of periodic and ordered three-dimensional porous structure with uniform pore size of 210 nm, the color of the film is bluish violet which is relative to the position of the band gap. By analysising of the microstructure, the course of the formation of flexible film was studied. In the stage of polymerization, the bulk shrinkage was more in the overlayer than in the interstitial spaces, due mostly to the mechanical resistance provided by the close-packed spheres. Stress difference between the surface and under sruface made the inverse film falled off from the ITO glass.This kind of film can be used for the preparation of flexible photoelectronic devices.Key words: