Abstract: At present, water controlling is still the main stable production measure in limestone reservoirs in Renqiu oilfield, yet, the water shutoff effect by adopting the conventional organic blocking agent is becoming poor gradually, therefore, a kind of heat-proof water shutoff agent with high strength is needed to plug the large pore path. TC-938 blocking agent can satisfy the demands of the above water shutoff technology, it not only can shut off water by the action of adsorption, but also can by the action of physical plugging, and is with good adhesivity. The agent has been used in wells in the oilfield for ll times, with the effective rate of 90. 9% and incremental oil of 6100 t. This has provided guaranty for the realization of stable production.