The low efficiency of dry carbonization for recycled concrete sand powder (RCSP) limits the utilization of RCSP resources. In this paper, the effects of wet carbonization treatment on the properties of RCSP and the influence of RCSP on the hydration and properties of cement paste at different replacement ratios were investigated. The results show that the CaCO₃ content in the wet carbonization recycled sand powder (WRCSP) is as high as 77.06% (mass fraction), and the CO₂ sequestration amount amounts to 0.53 kg CO₂ absorbed by each kilogram of RCSP. When the replacement ratio of WRCSP is 20% (mass fraction), 7 d compressive strength of cement paste is 45.3 MPa, showing increases of 76.3% and 4.61% compared to RCSP and PC, respectively. The main carbonization products of WRCSP are polycrystalline calcium carbonate and high polymerization silica gel, which can react with the hydration products of the cement, accelerate the early hydration of the cement, and significantly enhance the early mechanical properties of the cement. In summary, the higher the carbon fixation capacity after wet carbonization treatment is, the better the performance of WRCSP as a substitute for cement is. This conclusion verifies the feasibility of wet carbonization of RCSP and provide reference for future industrial applications.