Composite cementitious system of regenerated micropowder is beneficial for the application of regenerated micropowder. A binary/ternary cementitious composite system was constructed by using regenerated micropowder-Portland cement-fly ash. The effect of regenerated micropowder content on physical and mechanical properties of mortar test block was studied,and the hydration products and microstructure of mortar test block were investigated by XRD and SEM. The results show that with the increase of regenerated micropowder content,the compressive strength of test block at 3,7 and 28 d decreases,the water demand increases,the fluidity decreases,and the dry shrinkage decreases first and then increases. The drying shrinkage of composite cementitious system mortar test block mixed with regenerated micropowder and fly ash developes rapidly within 7～14 d. With the increase of regenerated micropowder and fly ash content,formation of C-S-H decreases gradually,and the internal pores and cracks of mortar test block increases significantly. The maximum total substitution rate of regenerated micropowder and fly ash to cement is 40%(mass fraction).