The invention discloses a crosslinking fluid loss agent preparation method. The method comprises steps of: adopting acrylic ester and acrylamide as main monomers of the crosslinking fluid loss agent and glycidyl acrylate as a crosslinking monomer of the crosslinking fluid loss agent, selecting a water-soluble radical initiator, and synthesizing a copolymer in the presence of nitrogen through adopting an emulsion polymerization method. The polymerization reaction time takes 2 hours, the insulation time costs 2 hours, the pH value is set to be 6-7, and the polymerization experimental reaction temperature is 70 DEG C. The copolymer prepared by the method can crosslink at the temperature of above 130 DEG C so as to form a proper crosslinking network structure, so that the viscoelasticity and temperature resistance of cement slurry can be improved, a problem of the poor temperature resistance of an acrylamide polymer which is served as a fluid loss agent can be solved, and the fluid loss reduction performance of the fluid loss agent in deep wells and ultradeep wells is improved. The crosslinking fluid loss agent mainly serves as the fluid loss agent for the well cementation cement slurry of oil-gas wells.