The invention discloses a planting method for simultaneous harvesting of ripe wheat and alfalfa seeds. The method comprises steps as follows: 1, diammonium phosphate is spread to be used as base fertilizer before seeding, the spreading amount is 20-25 kg/mu, and then ploughing operation and land preparation operation are performed; 2, underground drip-irrigation facilities are buried by an underground drip-irrigation pipe laying machine, inlaid type drip-irrigation belts are adopted, and the flow of drippers is 1.0-2.0 l/h; 3, winter wheat and alfalfa are seeded respectively by a grain drill seeder; the seeding rate of the wheat is 12-15 kg/mu, and the seeding depth is 3-5 cm; the seeding rate of the alfalfa is 1.0-1.5 kg/mu, and the seeding depth is 1-2 cm; the seeding time is from September 5th to September 15th, irrigation is performed twice before the winter, and the irrigation amount is 40-50 m<3>/mu each time; 4, irrigation is performed after the wheat and the alfalfa turns green, the irrigation period is 7-12 d, and the irrigation amount is 40-50 m<3>/mu; meanwhile, dressing of 20-30 kg of urea per mu is performed, dressing of 20 kg of monoammonium phosphate per mu is performed, and irrigation is performed for the last time from July 15th to July 25th; 5, the harvesting time is from August 1th to August 5th, a Gramoxone aqueous solution is sprayed before harvesting, 40-60 kg of water is added to 200-300 ml of the Gramoxone aqueous solution for spraying, alfalfa leaves are dewatered and dried quickly, harvesting is performed by a combined harvester after 4-7 d, and cleaning is performed by a separator in the step.