The present invention relates to a method for cultivating a functional stevia onion using a stevia liquid and an onion liquid using stevia. The method for cultivating a functional stevia onion can obtain a functional onion with excellent nutrient ingredients by forming a fermented liquefied fertilizer by adding fermented matter using the stevia and spraying the fermented liquefied fertilizer to a leaf surface so that the onion can absorb the onion. According to the present invention, the method for cultivating a functional stevia onion using a stevia liquid includes: a step of harvesting the stevia in August or September by cultivating the stevia and cutting the stevia so that the stevia including the dried leaf and stem are 6cm or less； a step of adding 40 liters of raw rice wine, 20 kg of sugar, 60 kg of onions, 10 kg of EM extract, and 1 kg of the stevia which is dried and cut, into a fermentation container for the liquefied fertilizer and fermenting and ripening the fermentation container at room temperature for at least 6 months by sealing the fermentation container； a step of removing any residue from the liquefied fertilizer solution fermented and ripened using a filter and storing the liquefied fertilizer solution in the container； a step of adding mold into a seeding tray port at the middle part and the last part of August and seeding an onion seed； a step of placing the seeding tray port on which the onion seed is seeded in a vinyl greenhouse and growing a nursery plant for 50-60 days； a step of forming a ridge by scattering an organic compost onto fields and paddies in which harvesting of single-cropping is finished on November and of carrying and planting the nursery plant grown in the tray port； a step of evenly spraying a diluted solution onto a leaf surface 6 times or more by diluting water in comparison with the stevia liquefied fertilizer solution stored in the container, at a dilution ratio of 1:1000 at intervals of 15-20 days before two weeks of o
