The invention belongs to the technical field of environmental monitoring, and particularly relates to a method for evaluating a flow pattern of constructed wetlands by using hydrogen or oxygen isotopic abundance. The method includes that contour line of the isotopic abundance of an area to be evaluated is drawn according to sampling point data obtained through measurement, and 2H (hydrogen) and 18O(oxygen) abundances are higher based on isotopic contour line. And an area forming obvious edges with other areas of the wetlands is a slow flow area or a dead water area, 2H and 18O abundances are relatively lower, and an area with little variation is a water flow passage of the wetlands. By the aid of the method, specific positions of the water flow passage and a stagnant area in the wetlands can be accurately marked, slow flow level is determined, limitation of a tracer agent adding research method and model simulation is overcome, the method is simple in sample preprocessing analysis, real and reliable in data results, and high in practicability.