Tahe oilfield in China belongs to fractured-vuggy carbonate reservoir with high temperature (100~130 celsius degree) and high salinity (two hundred thousand mg/L containing ten thousands mg/L of Ca2+ and Mg2+). After exploration for many years, the bottom water cones through fractures and vugs into production wells and then oil production declines obviously. In order to solve this problem above, a new inorganic composite blocking agent is proposed and developed in this paper. This new blocking agent is composed of superfine cement, strengthening agent, density adjusting agent, bridging agent, suspension dispersing agent, retardant and drag reducer. By adjusting the different proportions of components to make sure the density of this new blocking agent is in 1.00~1.10g/cm3 between oil (0.80~0.98g/cm3) and water (1.14g/cm3) which can build up packer existing in water-oil transition zone to control bottom water coning caused by gravity segregation resulting from density difference. Then the agent could expand sweep volume of bottom water and enhance oil recovery. This new blocking agent had been applied in one production well in Mar 2009, by Jul 2010, the accumulated oil increment is 1753.31t, the water cut decreased from 99.23% to 91.64% and the input-output ratio is up to 1:2.0. The success of field test confirmed that this new blocking agent is quite suitable for controlling bottom water coning and has a broad application prospect.