The invention discloses a facility and a method for siphon water changing in a reservoir by using rain-flood resources. The facility is characterized in that a collecting pool is arranged at the upstream dam toe of a reservoir dam, an apron is arranged at the downstream dam toe of the dam, a row of siphons are installed on the dam, and each siphon is connected by a water inlet pipe, a hump pipe, adrainage device and a water outlet pipe in sequence from the upstream to the downstream. When an upstream water level is higher than a downstream water level, control cabinets start water storage pools and water pumps to deliver water to the drainage devices, and the drainage devices initiate the siphons to siphon and release water. The facility uses the rain-flood resources to change water for the reservoir in a flood season, and negative pressure sensors and water outlet sensors are arranged on the siphons for intelligent control, so that the facility has the characteristics of safety, reliability, simple structure, all-weather siphoning water changing, large discharge flow, low energy consumption, easy operation, intelligent control and the like, and is an advanced water conservancy and environmental protection facility.