The invention relates to a water-fertilizer-seed integrated automatic seeder and a seeding method thereof, and belongs to the technical field of agricultural machinery. The water-fertilizer-seed integrated automatic seeder comprises a travelling device, a water spraying device, a seed discharging device, a fertilizer discharging device, a seed and fertilizer mixing device and an automatic seedingcontrol system. The travelling device comprises a bottom plate, front wheels and rear wheels. The bottom plate is provided with a motor, a battery, a range-extending power generator and a chain box. The water spraying device comprises a water tank, a water pump and spray nozzles. The seed discharging device comprises a seed discharging motor, seed dischargers and a seed guide tube. The fertilizerdischarging device comprises a fertilizer tank, a fertilizer discharging motor, a fertilizer stirring mechanism, a fertilizer discharging mechanism and a fertilizer guide tube. The seed and fertilizermixing device comprises seed and fertilizer cups and a fertilizer retaining cover. The automatic seeding control system comprises a PLC controller, an encoder and a counting sensor. Through precise control of seed discharge, fertilizer discharge, fertilizer drop, water spray, seed quantity and traveling distance, the linkage logic of components is clear, the seed discharge amount, fertilizer discharge amount and hole spacing are precise, the seed germination rate and seeding efficiency are high, and the adaptability is high.