Carbonated steel slag blocks were successfully prepared from pure steel slag, serving as the cementitious material, employing a low-cost sealed carbonation curing method. To further improve the performance of blocks, the preparation process parameters of blocks were optimized based on regression analysis and the impacts of water-solid ratio and forming pressure on the compressive strength and CO2 uptake rate of blocks were examined. The results of the study showed that the maximum strength of blocks could reach 82.70 MPa when the water-solid ratio was 0.13 and the forming pressure was 15 MPa. An optimum water-solid ratio exists at different levels of forming pressure, resulting in blocks with the highest compressive strength or CO2 uptake rate. Moreover, as forming pressure increases at different levels of the water-solid ratio, the compressive strength of the blocks increases while the CO2 uptake rate decreases. It is crucial to note that an important interaction effect exists between the water-solid ratio and forming pressure, which negatively impacts the compressive strength and CO2 uptake rate of the blocks. According to the regression model, the highest predicted compressive strength of the blocks was found when the water-solid ratio was 0.13 and the forming pressure was 15 MPa, and the highest predicted CO2 uptake rate of the blocks was found when the water-solid ratio was 0.14 and the forming pressure was 5 MPa. The relative errors between the measured and predicted values of compressive strength and CO2 uptake rate of the blocks under the two optimal parameter combinations are within a reasonable range, and the constructed regression model can effectively optimize the parameters of the block preparation process with good predictive ability.