In order to mitigate the negative impact of CO2 emitted by the cement industry on climate change, low concentration CO2 was used to mineralize the recycled fine powder produced in the process of recycling aggregates from construction waste, so as to partially replace the traditional cement with high carbon emission. In this work, the effects of different mineralization processes on the activity, water absorption and admixture adaptability of recycled hardened cement powder were studied, and the mineralization mechanism of recycled hardened cement powder with low concentration of CO2 was investigated. The results show that the performance of recycled hardened cement powder by direct aqueous mineral carbonation is much better than those of gas-solid carbonation. Compared with untreated regenerated micropowder, the water requirement of recycled hardened cement powder is reduced by 33%，and the hydration activity and additive adaptability are increased by 14% and 39% respectively. Property improvement of the recycled hardened cement powder by CO2 mineral carbonation is mainly due to the reaction of CO2 reacted with calcium hydroxide, calcium silica hydrate, ettringite and unhydrated cement clinker tricalcium silicate, dicalcium silicate to generate relatively dense calcite calcium carbonate (CaCO3, CC) and amorphous silica gel (SiO2·nH2O), refine the pores or microcracks , so as to reduce the water demand of recycled micro powder, and enhance the properties of the hydration activity and additive adaptability finally. The recycled micro powder after CO2 mineralization treatment can meet the requirements of JG/T 573-2020 Recycled Micro Powder for Concrete and Mortar to replace cement as a mineral admixture in a high proportion. While realizing the resource utilization of solid waste, CO2 is permanently fixed in the recycled micro powder, providing a new way for the deep decarbonization of the cement industry.