The invention discloses a method for measuring ecological niche differentiation of functional group seedlings on the light resource axis. The method includes the following steps that a field survey is made, and a sample plot is selected; the sample plot is equally divided, and patch type division is carried out; functional group division is carried out according to the photophilic character of different seedlings; corresponding indexes of the seedlings in all typical patch stages of the wild natural habitat are measured; corresponding indexes of the seedlings in all stages of artificial light control simulation are measured; the morphological structures and physiological and biochemical indexes of the seedlings are measured; ecological niche graphs of different functional group seedlings on the light resource axis are drawn. By means of the method, an important method is provided for quantification of ecological niche differentiation, an important basis is provided for explaining the dynamic mechanism of forest community succession, and important practical significance is brought to quantitative research of plant population ecology.