For medium and low permeability reservoirs, establishing effective displacement can improve the development effect of water injection and ultimate recovery. Based on the stable seepage model, the limit radius formula considering start-up pressure gradient and reservoir stress sensitivity is established, and combined with reservoir numerical simulation method, the variation pattern of sweep efficiency with different well spacing is studied. The relationship between permeability difference, injection-production well spacing and sweep efficiency is defined for the first time. The results show that the start-up pressure gradient has a great influence on the limit radius, which cannot be ignored for some medium and low permeability reservoirs. For multi-layer co-production reservoirs, the initial sweep efficiency and the final sweep efficiency differ greatly under the influence of permeability difference. Reducing well spacing can effectively improve sweep efficiency of medium and low permeability reservoir and ensure water injection efficiency, which finally improve oil recovery. Based on the research results, the oilfield infill adjustment is guided and better results are achieved,which provides reference for oilfield encryuption adjustment.