Abstract: The surface of aluminum hydroxide powder was treated with silane coupling agent at 70 ℃. The effect of silane coupling agent surface treatment on aluminum hydroxide was studied by sedimentation experiment, Fourier transform infrared spectroscopy characterization and water contact angle test. The results showed that the silane coupling agent was chemically coated on the surface of aluminum hydroxide powder, significantly improving the hydrophobicity and dispersion stability of the powder. Further, the mechanical, water resistance and flame retardant properties of low smoke and halogen-free flame retardant polyolefin cable materials filled with modified and unmodified aluminum hydroxide powder were studied. The results showed that the modified aluminum hydroxide powder filled in the cable material could significantly improve the mechanical properties, flame retardant properties and water resistance of the material. The elongation at break of the material increased from 150% to 200%; the maximum heat release rate during combustion decreased from 152.6 to 140 kW/m2. Moreover, with the increase of the amount of silane coupling agent treatment, the carbon layer of the material did not break after combustion, the second peak of heat release rate was delayed, and the peak value of the second heat release rate decreased. The microstructure of the material after immersion in water indicated that the silane modification of aluminum hydroxide could significantly reduce the erosion of water on the material, as shown by the change rate of elongation at break of the material after immersion in hot water increasing from −50% to −23.8%. Therefore, the bridging effect of silane coupling agents can improve the interface between aluminum hydroxide and the matrix resin, thereby enhancing the comprehensive performance of the material.