Water-retaining structures built with or on dispersive soil may easily be destroyed then after dangerous accidents associated with dispersive soil conditions, such as piping, caves and gullies, can occur. This study aims to propose a complete procedure to be followed when there is dispersive soil in water conservancy engineering or geotechnical engineering. The field investigations, empirical formulas and laboratory tests were conducted to define the dispersivity of Huaaopao soil samples. Among them, laboratory tests include pinhole tests, crumb tests, double hydrometer tests, pore water soluble cation tests and exchangeable sodium ion percentage tests. The dispersive mechanisms of the soil samples with dispersivity were analyzed from physical and chemical views. And the modified dose of lime on the dispersive soil samples was tested by pinhole tests and crumb tests. The results show that the soil samples TK4, TK8 to TK13 were dispersive, the soil sample TK15 was transitional, and the soil sample TK21 was not dispersive. The clay content of TK9 was less than 10% (physical level); the pH, the ESP and the PS were greater than 9.5, 7% and 60% (chemical level), respectively, resulting in its dispersivity. The TK4, TK8, TK10 to TK13 were dispersive only because of chemical factors with higher pH, ESP and PS. It is suggested to use 1 ~ 2% lime (mass fraction) to alter the dispersivity of dispersive soil samples in Huaaopao water conservancy project.