Abstract: The pressure coefficient of RX-1 oilfield in western South China Sea decreased severely due to the development and depletion, the formation energy was badly in need of supplement by injection water. Based on the analysis of formation water in RX-1, together with the experiment of static compatibility, dynamic compatibility and core compatibility, the authors chosen four types of water to be injected to conduct the study of compatibility. The experimental results show that formation water itself has the tendency of scaling; the compatibility of formation water with seawater, production sewage and well water is poor, the amount of scaling reaches the maximum when the mixture ratio is 7:3. There is little precipitation when the nanofiltration water is mixed with the formation water, and can effectively reduce the risk of scaling as demonstrated by the fact that the permeability decreased is less than 20% when the core displacement reaches 100 PV.