The hygroscopicity is one of principal factors affecting the long storage stability of red phosphorus smoke agent. To reduce the hygroscopicity of red phosphorus, the red phosphorus was coated by aluminium hydroxide/phenol formaldehyde resin. The process of preparing the coated red phosphorus was optimized by orthogonal test. The coating layer of red phosphorus was characterized by Fourier transform infrared spectrometer(FTIR) and scanning electron microscopy(SEM).Results show that the optimal process parameters for preparation of coated red phosphorus are: the molar ratio of formaldehyde and phenol 3:1, the mass of aluminum nitrate nonahydrate 0.05 g, the total mass of formaldehyde and phenol 0.4 g, the reaction temperature 30℃, the reaction time 3 h.The moisture absorption ratio of coated red phosphorus obtained reduces by 93.24%. The mass fraction of coating materials is below 4.5%.The moisture absorption rate of coated red phosphorus reduces remarkably as time goes on The coating materials are well coated on the surface of red phosphorus.