Water shutoff agent for oil well and preparation method of water shutoff agent

The preparation method comprises the following steps: uniformly mixing a modifier, a modified filler, acrylamide, 2-acrylamide-2-methylpropanesulfonic acid and deionized water, introducing nitrogen for protection, stirring, adding ceric ammonium nitrate, reacting, filtering to remove filtrate, and drying to obtain the water shutoff agent for the oil well, the water shutoff agent is of an organic-inorganic core-shell structure, rigidity, dimensional stability and thermal stability of inorganic materials can be fused with surface organic polymerization soft wet performance, the thermal stability and mechanical performance of the water shutoff agent are improved, and a side chain of a modifier contains a large number of quaternary ammonium salt cation structures; the quaternary ammonium salt cation structure can enhance the adsorption effect of the water shutoff agent and a sandstone layer, so that the water shutoff agent can be firmly fixed on the sandstone layer, and the organic silicon chain segment on the ma