Disclosed is a method for measuring nutrient competition of the kindred plants under water planting. By the method, an experiment 1 and an experiment 2 are performed at the same time. The experiment 1 is performed by selecting a stock plant A and a stock plant B of the kindred plant to be cultivated in a kindred-plant nutrient competition measuring device under water planting. Different from the experiment 1, the experiment 2 selects two plants from the stock plant A. The method includes calculating competition intensity index of non-relative plants for nutrients in the water by the measured nutrient content of the stock plants, if the index is larger than zero, determining that the kindred plants have nutrient absorption competition relation, and selecting the distribution mode of the non-relative plants when the water is purified by hydroponic plants; otherwise, selecting the distribution mode of the relative plants; if the index is equal to zero, selecting any one of the distribution modes. The method can conveniently determine the competition relation among the non-relative modes and can select the advantageous plant distribution mode having good nutrient absorption effect in the water to be applied to water purification in the water ecological restoration.