Abstract: The influence of soluble alkali on hydration heat and setting time of the cement mixing the polyether type polycarboxylate-based superplasticizer (PC-1) and the polyester type polycarboxylate-based superplasticizer (PC-2) have been investigated, and the hydration products are examined with X-ray diffraction analysis. The results show that appropriate increase soluble alkali can reduce the hydration exothermic rate and heat, shorten the formation time of AFm phase, and accelerate the hydration process of cement. When PC-1 dosage is low, a spot of soluble alkali have retarding effect on paste, but overdose resulted in accelerating its setting. When PC-1 dosage is high, soluble alkali can accelerate setting of paste, but for the paste mixed with PC-2, increasing soluble alkali content can shorten the paste setting time greatly. CH phase content increased significantly when the cement mixed with PC-1, and soluble alkali can further promote the depth hydration of C3S and C2S. However, when the cement mixed with PC-2, increasing soluble alkali content can slow down the late hydration of cement.