Some low permeability reservoirs in China have been effectively developed by water flooding，but with insufficient sweep. Thus，it is urgent to study the evaluation method of water-flooding plane sweep. The flow tube model is a good method for rapid evaluation of water-flooding plane sweep coefficient. An improved flow tube model that considers the threshold pressure gradient，anisotropy，artificial fracture，non-piston displacement，and irregular well pattern was developed. A fast calculation module for the water-flooding plane sweep of low permeability reservoirs was created，based on the modified flow tube model，to study the influence of well patterns，well array ratios，and anisotropy on the water-flooding plane sweep coefficient. Consequently，unsuccessful water injection into injectors and oil production from producers can be attributable mainly to poor physical properties of low permeability reservoirs and threshold pressure gradient. An optimal well array ratio can be found under different anisotropies，and the optimization chart in different well array ratios in low permeability reservoirs is proposed. During the production process，attention should be paid to the perfection of the well pattern and the in-time filling of holes to improve the injection-production correspondence.