The invention discloses a water planting method for stylosanthes guianensis. The method comprises the following steps of growing seedlings, preparing marcoelement mother solution and microelement mother solution, preparing water planting nutrient solution for the stylosanthes guianensis and water planting. Marcoelements comprise KNO3, Ca(NO3)2, MgSO4.7H2O; microelements comprise ZnSO4.7H2O, CuSO4.5H2O, FeSO4.7H2O and Na2-EDTA; the step of preparing the water planting nutrient solution for the stylosanthes guianensis comprises the following flows of weighing 76ml of the marcoelement mother solution and 19ml of the microelement mother solution, and evenly mixing the marcoelement mother solution and the microelement mother solution with 19L of purified water or distilled water; when the water planting is performed on the stylosanthes guianensis, a shading net of which the shading coefficient is 50 percent is erected, and gas is rushed into the water planting nutrient solution for the stylosanthes guianensis by an aerator for ten minutes every two days. According to the method, various different or numerous level tests can be completed at a time simultaneously; complex processes of open field culture and soil preparation, watering, weed removal and the like are replaced, and the sampling operation is convenient.