The study on dispersion mechanism of dispersive soil has attracted attention in water conservancy project. In order to investigate the main dispersive influencing factors of soil, grey correlation degree method was used to analysis the relation between dispersion degree and exchanging sodium percentage, clay particles content, organic matter, PH, specific surface area, structure damage rate, cation exchange capacity. The results show that the cation exchange capacity and exchangeable sodiuma do the best contribution to the dispersion of soil, and the specific surface area and the structure damage rate influenced the dispersion slightly.