Many multilayer sandstone reservoirs have reached extreme high water content and high recovery stage after long time waterflooding. These inner LPTOLs have been the main potential reserves. Lean-stratified water injection is one of the most important technologies to increase production and develop potential for multilayer oilfields with extreme high water content. However, traditional models cannot entirely solve the inner boundary conditions of lean-stratified water injection. Therefore, we established the injection wellbore constraint equations, which were coupled with the oil/water two-phase numerical reservoir models. Upon an embedded fracture model for simulating hydraulic fractures, a method to simulate the reservoir with horizontal fractures is shown. The influences of reservoir and fluid, horizontal fractures, and injection-production characteristics are analyzed for oil production and water-content dynamic. Considering the specific situation of lean-stratified water injection wells, the influences of different segments numbers, modes of combination in segment layers, and rhythm characteristics of remaining oil reserves and distribution are evaluated.