In order to prepare well-ordered micron and submicron grating fold structures for simpler stress measurement, tunable grating was prepared by a self-assembly process based on a rigid film/flexible substrate. A polydimethylsiloxane (PDMS) substrate was prepared on polyethylene (PET) by the spin-coating method; then, the curved PDMS-PET substrates were processed in oxygen plasma. After appropriate surface treatment time in plasma, the curved substrates were flattened, and well-ordered wrinkling shape gratings were obtained due to mechanical buckling instability. Then, according to the principle of grating spectral, proper stress measurement can be achieved when a tunable grating structure was used for stress testing. The experimental results show that: When the curvature radius of the grating is 1.4 mm, the wavelength of the tunable grating folds prepared from 0 to 10% of the strain ranges from 452 to 507 nm; when the radius of curvature of the grating is 5.6 mm, the wavelength of the tunable grating folds prepared from 0 to 15% of the strain ranges from 498 to 572 nm. The proposed method of tunable grating fabrication is a low cost, simple process and enables mass production technology. It is a potential method to prepare variable spacing grating. Its expected applications in future include spectrometry, optical communication, and other related fields.