Polymer/viscosity reducer combination flooding has been widely used in many oil fields and has obtained very good performance. However，as the increase of oil viscosity，the incremental oil production decreases. By far，there is no determination method of the upper limit of oil viscosity suitable for the polymer/viscosity reducer combination flooding，which severely restricts the wide application of this chemical flooding. Taking the oil increment value for a ton of agent as the standard，a determination method of the upper limit of the oil viscosity for the polymer/viscosity reducer combination flooding was built based on the financial net present value. Taking the Ng41-51 unit in eastern area of Gudao Oilfield for example，a chart was obtained to determine the upper limit of oil viscosity. The results show that the upper limit of oil viscosity increases along with the increase of oil price. If the oil price is 40 $/bbl，the upper limit of oil viscosity is only 854 mPa?s. Howev? er，if the oil price is 70 $/bbl，the upper limit of oil viscosity increases to 4 471 mPa?s.