The invention relates to a sewage purifying and automatic backwashing sewage discharge device. The device is mainly used for purifying sewage. The device comprises a water inlet funnel, a reverse siphon pipe and a positive siphon pipe, wherein a buoyancy valve device is arranged at the bottom of the water inlet funnel; the bottom of the water inlet funnel is communicated with the top of a descending section of the reverse siphon pipe, the bottom of the reverse siphon pipe is a sediment section of the reverse siphon, both ends of the sediment section of the reverse siphon pipe are respectively communicated with the descending section and the ascending section of the reverse siphon pipe, the other end of the ascending section of the reverse siphon pipe is communicated with the water outlet section of the reverse siphon pipe, the descending section and the ascending section of the reverse siphon pipe are communicated through a middle pipeline, a first waterpower valve device is arranged in the middle pipeline, and a second waterpower valve device is arranged at the bottom in the descending section of the reverse siphon pipe; one end of the inlet section of the positive siphon pipe is communicated with the side wall of the middle part of the descending section of the reverse siphon pipe, the other end of the inlet section of the positive siphon pipe is communicated with the ascending section of the positive siphon pipe, the other end of the ascending section of the positive siphon pipe is communicated with the water outlet section of the positive siphon pipe, a filter device is arranged in the inlet section of the positive siphon pipe, and the highest point of the reverse siphon pipe is higher than that of the positive siphon pipe.