In order to improve the early performance of cement-fly ash system， the effects of diethanol-monoisopropanolamine （DEIPA） and calcium silicate hydrate crystal nucleus （C-S-H-PCEs） on the setting time， fluidity and compressive strength of the system were studied. X-ray diffraction （XRD）， thermogravimetric-differential scanning calorimetry （TG-DSC） and scanning electron microscopy （SEM） were used to investigate the mechanism of the two early strengthening agents. The results show that the combination of the two early strengthening agents can shorten the setting time， increase the fluidity and enhance the compressive strength. The combined effect of 0.03% DEIPA and 2.00% C-S-H-PCEs is the best， the fluidity increases by 217.5 mm， the initial and final setting time decreases by 120， 127 min， respectively， and the compressive strength increases by 6.6， 6.1 MPa at 1，3 d， respectively.