Influence of different factors on rheological properties of cement mortar was investigated using rotational viscometer, and the relationships between the plastic viscosity, yield stress, thixotropy and fluidity of cement mortar were studied. The results show that when the fluidity is 134300mm, the rheological characteristic of cement mortar conforms to Bingham model. Although the factors of water cement ratio, aggregate cement ratio, mineral admixtures, and chemical admixtures have different effects on plastic viscosity, yield stress, and thixotropy of cement mortar, they do not change the rheological model of cement mortar. The correlation between plastic viscosity, yield stress and fluidity of cement mortar is weak,but there is a correlation between thixotropy and fluidity of cement mortar.