The invention discloses an insulated gate bipolar transistor (IGBT) and a manufacturing method thereof. The IGBT comprises an N-type base region, a P-type base region, a back P+ emitter region, an N+ collector region, a gate oxide, a collector electrode, a gate electrode and an emitter electrode; the N-type base region consists of a N+ diffusion residue layer, a N- base region and an N+ buffer layer which are sequentially laminated; and the dosage concentration of the N+ diffusion residue layer and the N+ buffer layer is gradually increased outwards from a boundary with the N- base region. In the IGBT of the invention, a front surface of the N- base region is provided with the N+ diffusion residue layer, so that the ion dosage concentration of a N-type front surface is improved and the influences on a Junction Field Effect Transistor (JEFT) resistor are reduced; therefore, the voltage drop of the IGBT under a conducting condition is effectively reduced.