Liquid extraction is a common production measure in the middle-late stage development of water injection oilfield. By increasing the production pressure difference, some crude oil with high starting pressure in low permeability reservoirs or regions can participate in the flow, expanding the sweep efficiency. However, due to the lack of deep understanding of the micro mechanism of liquid extraction, the production performance of oil wells after liquid extraction shows obvious differences in field practice. Taking a domestic sandstone oilfield as the research object, the mechanism of improving the development effect of liquid extraction is studied from the perspective of porous level through NMR experiments, and then combined with typical model, the numerical simulation of liquid extraction is conducted to simulate the influence of different crude oil viscosity and planal reservoir heterogeneity on liquid extraction, to determine the theoretical mechanism of liquid extraction amplitude and timing. Finally, according to the actual geological and fluid characteristics of the oilfield, the classified liquid extraction strategy of each reservoir is studied. This study summarized the mechanism of fluid extraction to improve the degree of remaining oil production under the influence of reservoir heterogeneity from both micro and macro perspectives. It is pointed out that the main mechanism of microscopic liquid extraction is to overcome the seepage resistance due to capillary effect and Jamin effect in small pores, and there are optimal liquid extraction amplitude and time. Macroscopically, there are differences in fluid extraction conditions for different crude oil reservoirs, and the objective differences in fluid supply capacity of the reservoir itself determine the material basis. The influence of reservoir heterogeneity on liquid extraction is that the location of the oil well directly determines whether it is suitable for liquid extraction and the effect of liquid extraction. The research has guiding significance for the middle-late stage liquid extraction development of similar water injection reservoirs, including: the liquid extraction wells can be optimized according to the heterogeneous conditions of the reservoir and the configuration relationship of the injection production well pattern, and can be used to make decisions on reasonable liquid extraction methods under different physical properties.