The rationality of injection-production ratio is important to the production performance of gas flooding. According to concepts and research results of the material balance principle，Darcy’s law，fractional flow theory，oil production rate multiplier due to gas flooding；and“oil wall”description of gas flooding，and by considering the quantified factors including gas injection dissolution，reservoir fluid expansion，mineralization and solidification of injected gas，reservoir pressure-sensitive effect，natural fracture drainage and dry layer suction，liquid exchange between gas injection areas and external environment，and the composition of produced gas oil ratio，the formula of injection-production ratio based on underground two-phase volume of the produced oil-water（2P formula）and underground three-phase volume of produced oil-water-gas（3P formula）are proposed，respectively，and the calculation method of daily gas injection rate is proposed as well. The new method is applied to study the injection-production ratio change of representative CO2 flooding projects in extralow permeability oil reservoirs. It is found that it is feasible to allocate injection rate according to the injection-production ratio estimated by the 3P formula after continuous gas injection（CGI），and to allocate injection rate of water-alternatinggas（WAG）injection according to the injection-roduction rate estimated by 2P formula.