Abstract: Clay slurry was treated through magnetization. The characteristics of the physical property change of the clay slurry after magnetic treatment such as viscosity, density, pH value, conductivity, syneresis rate, concretion rate and anti-permeability were studied. After magnetic treatment, density, viscosity and syneresis rate of the clay slurry decrease, pH, conductivity and concretion rate increase, the syneresis rate and the concretion rate are improved with the magnetization time. The magnetic treatment improves the rheological property of clay slurry, the anti-permeability performance of the cemented body of clay slurry after magnetic treatment rises greatly compared to the cemented body of clay slurry not treated by magnetization. After the magnetic treatment, the Zeta electrical potential and pH of the clay slurry increase, resulting in increase of dispersion, reducing the syneresis rate and increasing the concretion rate. The improvement of anti-permeability performance of the same quality clay slurry benefits from the significant increase of the concretion rate of the magnetically treated clay slurry, while the decrease of its viscosity results from the strong repulsion among the particles of clay slurry after the magnetic treatment.