The present disclosure provides a method for preparing a semiconductor die structure with air gaps for reducing capacitive coupling between conductive features and a method for preparing the semiconductor die structure. The method includes: forming a first supporting backbone on the substrate; forming a first conductor block on the first supporting backbone; forming a second supporting backbone on the substrate; forming a second conductor block on the second supporting backbone; forming a third conductor block suspended above the substrate and connected to the first conductor block and the second conductor block; sequentially forming an energy removable layer and a capping dielectric layer over the substrate, and the energy removable layer and the capping dielectric layer separating the first conductor block, the second conductor block and the third conductor block; and performing a heat treatment process to transform the energy removable layer into a plurality of air gap structures.