Abstract: To investigate the effect of ambient temperature and hydration time on rheology of nano-metakaolin(NMK) cement pastes, the rheology variation of NMK cement pastes with different ambient temperatures(8~45℃) and hydration time(10~90min) was studied by rheological method.Meanwhile, X-ray diffractometer and particle size analyzer were used to analyze the early age hydration properties and flocculation structures of fresh NMK cement pastes.The effects of ambient temperature, hydration time, NMK content and water-to-binder ratio were taken into consideration, a rheological parameter prediction model was established based on BP neural network.The results demonstrate that the cement hydration is slowly at 90 min after contact between cement and water, the NMK particle properties and flocculation structures are the main influential factors of rheological properties.The rheological characteristic of NMK cement pastes conforms to modified Bingham model, and the pastes show shear thinning behavior.With the increase of temperature(8~45℃),the apparent viscosity decreases, thixotropy first increases and then decreases, and the thixotropy reaches the peak at about 27℃;the yield stress and plastic viscosity have not much changed with ambient temperature.The effects of hydration time(10~90min) on the apparent viscosity, yield stress and plastic viscosity of cement paste were weakened by 1%~10% NMK addition.The predictive results of BP neural network model are in good agreement with the experimental results.