Abstract: Gas breakthrough has significant affect on gas cap reservoir,so it is important to avoid gas breakthrough and keep steady of gas/oil interface during developing.On the base of actual conditions of Lamadian oil field,using the simulation experiment method,the development effects of Lamadian reservoir were studied when water,polymer and polymer gel are regarded as barrier fluid respectively.The experiment shows that the factor which influence development effects of barrier water flooding include the size of slug,the pressure of gas cap and recovery rate of oil.If develop gas cap reservoir by inject water will decline concentration of polymer and cause the decrease of barrier capacity.On the bases of analyzing these influence factor,it point out that polymer gel is the best barrier fluid.