The cementitious pastes were prepared with the fly ash replacements of 0~60% at a fixed water-binder ratio of 0.4 and cured at various constant temperatures of 20℃, 24℃ and 28℃ for measuring setting time, the electrical resistivity and the compressive strength.The results from the setting time, the peak occurrence of the electrical resistivity rate development and strength gain show the delay effect of fly ash replacement and acceleration effect of temperature on hydration.The compressive strength (fcu) and the resistivity (p) of the pastes at 2d at each temperature follow a good positive linear relationship, which are fcu=2.0453p-7.9021 (R2 =0.9935) at 20℃,fcu=0.9627p-2.1451 (R2 =0.9825) at 24℃, fcu=0.5387p-2.0472 (R2 =0.97) at 28℃.The smaller slope value from fcu vs.p was obtained in a higher temperature blended hydration system, which shows that the resistivity development is more sensitive to temperature change than strength.The XRD and SEM observation reveals that fly ash does not react in early age acting as fillers to dilute cement.The setting time and compressive strength of a cementitious hydration system at different temperatures can be estimated and predicted by electrical measurement.