Shengli oilfield has rich resource of thickened oil. In order to improve the recovery ratio of steam huff and puff, the controllable quantitative requirement of layering steam injection technology can be realized by the controllable quantitative injection allocator designed according to the principle of layering steam injection technology. In order to further understand the flow inside the valve and confirm the pressure differential range required for maintaining the constant flow, FLUENT hydromechanics software was applied to conduct the numerical simulation study of the internal flow field of permanent flow valve. The research results show that as for the flow inside valve with the fluid medium of water, the peak flow rate occurs at the gap between the floater and fixed pore plate; and under this gap, the backflow is formed. The fluidic divergence phenomenon occurs in the downstream area; two swirls are formed and consume the energy of mainstream movement, which will lead to the pressure drop and energy reduction. The variation range of outlet and inlet differential pressure (Δp) required for maintaining the constant flow rate (Q=0.5 m3/h) is 900~7 400 Pa.