The invention relates to the technical field of spillways, in particular to a reservoir spillway and a flood discharge method. The reservoir spillway mainly comprises a vertical shaft and a water outlet channel vertically connected to one end of the vertical shaft. A plurality of siphon pipelines are arranged at the upper end of the vertical shaft in the circumferential direction. One end of eachsiphon pipeline is arranged on the outer wall of the vertical shaft and is a drainage section. The end face of each drainage section is lower than the upper end face of the vertical shaft. The other end of each siphon pipeline is a discharge section. The discharge sections are arranged on the inner wall of the vertical shaft and spirally distributed downwards towards the bottom of the vertical shaft in the circumferential direction. The reservoir spillway and the flood discharge method have the advantages that flood falling into the vertical shaft can fall spirally through the spirally distributed discharge sections, energy is gradually dissipated when the flood moves, impact of the flood on the shaft bottom is reduced, and therefore the probability of damage to the vertical shaft is reduced.