In this paper, the fractal structure evolution of aluminum hydroxide colloid particles under aging time 0 - 135 minute was investigated by using synchrotron radiation SAXS technology and other potential characterization methods, including FTIR, SEM, DLS, and Zeta potential.The possible growth mechanism was proposed. The scattering double logarithmic coordinate plots under different aging times showed obvious linearity, indicating that significant differences in the fractal structure of the samples. With the extension of aging time increased from 25 minute to 85 minute, the mass fractal dimension Dm increased from 2.29 to 2.78. The Dm values were in the range of 2.76 - 2.79, with little change between 95 and 135 minutes. This indicated that the primary particles of the system will rapidly reunite from the initial relative dispersion state to larger size clusters and finally form dense gels at the aging time 25 minute - 85 minute. The gel process had been completed, the size of the colloid particles did not change during 95 -135 minute, and the adhesive block may break at 135 minute.