Abstract: It is known that the method of magnetic treatment can be used to improve the performance of cement slurry. The test instruments, reagents and experimenting methods are presented. By measuring the zeta potential between cement granules before and after magnetization, it shows that under the premium magnetic induction strength of 0.23T, the absolute value of zeta potential after magnetization increased by 2.5mV. Six conventional cement additives are also tested, and the increases of absolute value of zeta potential range from 5~40mV. The test provides the theoretical evidence for interpreting why magnetic treatment can improve the performance of cement slurry.