The invention relates to a cultivation method of a medicinal plant, especially to a production method of a water planted motherwort and a dedicated nutrient solution thereof. According to the invention, the motherwort is cultivated with only a hydroponics period of 45 days, thereby enabling continuously producing for 8 batches for the whole year. Standardize cultivation can be realized in the true sense because light, temperature, fertilizer, water and the like can be manually controlled during the whole process, and the quality is stable in each batch. The content of stachydrine hydrochloride in the motherwort can reach to 1.94 % through reasonably regulating the nutrient solution, combined with corresponding hydroponics measures, and biomass and alkaloid content can be effectively improves by adding L-proline at a specific period, wherein the highest content of the stachydrine hydrochloride can reach to 2.26%, more than 5 times of requirements in 2010 edition pharmacopeia. The method has an important role for solving problems that the quality of the current motherwort decreases and is unstable, and that manufacturer demands fresh motherwort year in year out.