In the process of water injection development of western of the south China sea oilfield, the serious barium/strontium sulfate scales have occurred in the oil wells in the middle block of the oilfield, due to the incompatibility between injected sea water with rich SO42-and formation water with rich Ba2+and Sr2+. The experiment was conducted for four kinds of organic phosphonate scale inhibitors in terms of chemical compatibility of barium strontium sulfate scale inhibitors, static inhibition efficiency, stability and dynamic adsorption/desorption of the scale inhibitors required for squeeze treatment. The experimental results showed that: by adjusting the pH chemical compatibility of HYZ-121 scale inhibitor was better at 120℃; when concentration ≥5mg/L,static inhibition efficiency＞90%；under the 120℃ heat treatment after 30 days, the drop of inhibition efficiency is very small, still＞90%; the results of core flood experiment showed that at low pH the adsorption/desorption performance of scale inhibitor was better than at high pH. The reasonable scale inhibitor HYZ-121 was selected to solve the problem of the western of the south China sea oilfield.