In this paper, we firstly report a GaN-based bipolar diode with a p-n junction generated by Three-Dimensional Electron Sea and Three-Dimensional Hole Sea which are induced by elaborately designing the graded AlGaN layer. According to the experiment-calibrated simulation, the proposed device features a high forward current of 2.83 A/mm and a maximum breakdown voltage (BV) of 112 V in a very small chip area. Moreover, this diode has a fast reverse extraction process and reverse recovery time of 2ns. Considering the selective etching technique and selective area regrowth technique are mature for GaN-based materials, although this design needs more trade-off and optimization to balance the on-state current and BV, the strong capability in current transportation and a high performance in dynamic recovery enable a notablely promising prospects in various power applications.