The invention discloses a back surface structure of an IGBT chip, an IGBT chip structure and a preparation method thereof. The back surface structure comprises: a buffer layer and a doped layer, the doped layer is formed by ion implantation in the buffer layer; the doped layer of a terminal region and a transition region is subjected to high-temperature annealing treatment; a doped layer of the active region is subjected to twice high-temperature annealing treatment to achieve different hole injection efficiencies of the active region and the terminal region so as to improve the current concentration problem in the IGBT transition region and improve the reliability. Compared to the prior art of a treatment mode that a photolithography process is used to implant different doses of doping ions on the back side of the active region and the terminal region to achieve different injection efficiencies of the back surface collectors of the active region and the terminal region, the back surface structure of the IGBT chip, the IGBT chip structure and the preparation method thereof only employ the annealing process to omit the photolithography process so as to save the manufacturing cost. An inert ion defect layer is implanted in the buffer layer to form a defect layer, so that the IGBT back surface collector can adopt a higher doping concentration, and the IGBT back surface and the back surface metal easily form good ohmic contact, thereby reducing the IGBT on-state voltage drop.