An effluent discharge simulating and denitrifying experiment device for a rural septic tank is disclosed. An original-sample water container contains original sample water of the septic tank. The original sample water is fed into an automatic sample injector. A siphon is disposed in the automatic sample injector. One end of the siphon extends out of the bottom of the automatic sample injector and is connected to a water distributor, and the other end of the siphon is disposed in the automatic sample injector. The water distributor is a sealed container full of the original sample water of the septic tank. A plurality of water distributing pipes are inserted into the water distributor from the upper part of the water distributor. The other end of each of the water distributing pipes is connected to a corresponding septic tank original sample water experiment bottle. The experiment bottles are connected to a denitrifying gear. The inner cavity of a denitrifying box is provided with a plurality of separating walls according to the water flowing direction. Denitrifying bacterium carriers are disposed in separating cavities. The device can simulate effluent discharging conditions of the rural septic tank, achieves automatic effluent discharging simulation, can perform a plurality of groups of repeat experiments simultaneously, is high in efficiency and is advantaged by having a septic tank effluent denitrifying function.