The invention discloses a high-temperature salt-resistant fluid loss additive modified gum resin for drilling fluids, wherein the resin is prepared from the following raw materials: 220-240 parts of clear water, 30-40 parts of sodium methylallyl sulfonate, 10-15 parts of N,N-dimethylacrylamide, 0.5-1.0 part of a temperature-resistant monomer, 20-30 parts of methacryloyloxyethyl trimethyl ammoniumchloride, 3-5 parts of a chelating agent, 0.5-1.0 part of an initiator, 25-35 parts of a gum resin, 8-10 parts of a 40% sodium hydroxide solution, 5-10 parts of propylene oxide and 10-20 parts of an additive, wherein the temperature-resistant monomer is 4-vinyl guaiacol, the chelating agent is sodium citrate, the additive is polyvinyl alcohol powder, and the initiator is a combination of an azo initiator and a redox initiator. According to the invention, the high-temperature salt-resistant fluid loss additive modified gum resin has good temperature resistance, good salt resistance and environmental protection performance, solves the problems of poor temperature resistance, poor salt resistance, high production cost and complex process of the fluid loss additive in the existing drilling process, has strong biodegradability, and effectively reduces the pollution to reservoirs and environments.