The present invention relates to a community optimization method of a low efficiency-water conservation forest. The method comprises the steps of surveying an indigenous plant community, and determining the current and historical distribution of the indigenous plant community; evaluating the plant community, and screening a plurality of introduction after-culture species facilitating improving a water conservation function; configuring two varieties or more than two varieties of trees of different ages for the landscapes of the low efficiency-water conservation forest according to the above screened introduction after-culture species to increase the degree of heterogeneity of the plant community in the horizontal space; managing the low efficiency-water conservation forest according to the main characteristics and the degeneration reasons of the community of the low efficiency-water conservation forest. The method of the present invention enables the water conservation function of an ecological system to be improved, at the same time, considers the coupling functions, such as the biodiversity protection, the soil conservation, etc., and promotes the healthy, stable and long-term development of the ecological system.