Belonging to the technical field of oilfield exploitation and drilling treatment agents, the invention discloses a high temperature resistant filtrate loss reducer for drilling fluid and a preparationmethod thereof. The high temperature resistant filtrate loss reducer comprises: 30-60 parts of humic acid resin, 10-50 parts of acrylamide, 10-40 parts of acrylic acid, 10-30 parts of 2-acrylamido-2-methylpropanesulfonic acid, 10-20 parts of maleic anhydride, 5-20 parts of N-vinyl pyrrolidone and 5-10 parts of a nano-material. The filtrate loss reducer disclosed by the invention is formed by graft copolymerization of corrosive acid resin and other monomers, and contains the nano-material, can effectively improve the temperature resistance and salt resistance of the filtrate loss reducer, andensures good performance under the conditions of a high temperature of 220DEG C and high salt.