The activate effect of various activator on fly ash was studied according to the comparative tests of cement strength. The result shows that the sulfate activator and alcohol amine activator composite mixture has the best activate effect under the reasonable mix ratio. The composite mixture can obviously affect fly ash cement strength, and under the 50% mixing amount of fly ash, the 3d strength of cement is improved by 30% to 50%, and the 7d strength of cement is improved by 20% to 30%. Activate mechanism of the composite activator was studied through the XRD, SEM and other microscopic testing methods.