Abstract: In this paper, butane tetracarboxylic acid esterified galactomannan(EGM) was used as paper strengthening agent. Equally, antimony trioxide and magnesium hydroxide were used as flame retardants. Then, the effects of their compounding methods on the strength and flame retardancy of flame retardant paper were studied. The results showed that the addition of EGM could improve the tensile index, bursting index and folding resistance of flame retardant paper. When 1.5% EGM and 15% magnesium hydroxide were added, the tensile index of flame retardant paper reached 56.2 N·m/g, the bursting index reached 3.37 kPa·m²/g, and the folding resistance reached 46 times, respectively. Notably, compared with the flame retardant paper without EGM, tensile index, burst index and folding endurance increased by 14.7%, 12.0% and 119.0%, respectively. Particularly, when the addition amount of antimony trioxide was 15%, the addition of magnesium hydroxide was 25%, the flame retardant effect of the paper reached the best, namely, the carbonization length of the flame retardant paper was 16.8 mm, the continuous burning time was 0.43 s, and the ignition time was 25.96 s. SEM and EDS analysis showed that magnesium hydroxide and antimony trioxide were successfully attached to the paper fiber. The addition of EGM enhanced the retention of magnesium hydroxide and antimony trioxide on the paper surface and the adhesion between paper fibers. TG curves showed that the addition of antimony trioxide and magnesium hydroxide increased the initial decomposition temperature of the paper, and the amount of carbon formed at 600 ℃ increased from 0.34% of the control to 15%.