The invention provides preparation of a clay anti-swelling agent with an oil washing effect and for water injection. According to the clay anti-swelling agent, the composition use of a self-synthesized clay anti-swelling cationic surfactant and cheap ammonium phosphate, ammonium chloride and potassium chloride is disclosed, and the agent has the better capability of preventing hydration and swelling of clay particles; in composition with dodecyl ethoxy betaine and propylene glycol polyoxyethylene polyoxypropylene ether demulsifier, the clay anti-swelling agent not only has the oil washing function but also prevents emulsification and achieves the effect of avoiding the situation that blockage damage is caused by emulsification during oil washing; in composition with a trimethyl-1-propanaminium iodide surfactant, the clay anti-swelling agent has the excellent capability of reducing surface tension and interfacial tension and greatly reduces and prevents water lock damage. Thus, the developed clay anti-swelling agent has the triple effects of preventing clay swelling, reducing the surface tension and the ultra-low interfacial tension to prevent water lock and to wash oil, and the agent plays an innovative demonstration role in developing the multifunctional clay anti-swelling agent for water injection.