The invention discloses a synchronous fertilizing and seeding machine and an operating method thereof. The synchronous fertilizing and seeding machine comprises a seed and fertilizer tank, fertilizingpipes, seeding pipes, a bottom plate, double drill legs and a furrow plough. The seed and fertilizer tank is arranged on the upper surface of the bottom plate, and a partition is arranged in the seedand fertilizer tank to partition the seed and fertilizer tank into a fertilizer tank and a seed tank. Each double drill leg is formed by welding of two abreast drill legs, and the double drill legs in a row are arranged in the middle of the lower surface of the bottom plate. A plurality of fertilizer dischargers and seed dischargers are arranged at the bottom of the seed and fertilizer tank and staggered at intervals on a same transmission shaft. Each double drill leg is connected to one fertilizer discharger and one seed discharger through one fertilizing pipe and one seeding pipe. The seeddischargers are communicated with the seed tank, and the fertilizer dischargers are connected with the fertilizer tank. By design of the partition in the middle of the seed and fertilizer tank, fertilizing and seeding can be realized through one shaft, so that structural simplification is realized. Due to adoption of the double drill legs, fertilizing and seeding can be performed by use of the drill legs in a row, and structural simplification and size reduction are realized.