The utility model relates to the technical field of photodiodes, in particular to an avalanche photodiode with a three mesa structure, which comprises a buffer layer, a substrate and a plurality of reinforcing structures, and a P-shaped contact layer is arranged above the buffer layer, The first table top, the second table top and the third table top are arranged above the P-type contact layer from top to bottom. The passivation layer is arranged between the first table top, the second table top, the third table top and the P-type contact layer. A plurality of strengthening structures are respectively arranged at the substrate and the passivation layer. The strengthening structure includes the strengthening layer and the withstand voltage layer. The strengthening layer is bonded with the withstand voltage layer and is located on the outer diameter of the withstand voltage layer. The withstand voltage layer is bonded with the passivation layer and is located on the outer diameter of the passivation layer. The withstand voltage layer is also bonded with the substrate and is located on the outer diameter of the substrate. Through the strengthening layer and the withstand voltage layer, the exterior of the avalanche photodiode can be protected, thus reducing the damage rate of the avalanche photodiode.
