The performance of concrete is greatly affected by recycled coarse aggregate (RCA). Understanding how they affect performance of concrete is crucial to maximizing RCA utilization, reducing carbon emissions in the construction industry, and contributing to achieving national carbon peaking and carbon neutrality targets. Four groups images of aggregate characteristic of lithium slag recycled aggregate concrete with different RCA replacement rates were acquired by using CT scanning. The shape factor (SF), angularity (AN), angularity and surface texture (AT index), and three-dimensional sphericity (SP) were calculated by using digital image processing techniques. Based on the analysis of their distribution rules and characteristics, a gray correlation analysis method was used to determine the relationship between different aggregate characteristics parameters and compressive strength. The results show that the RCA has a higher irregularity, and its surface is rough and angular due to the different amounts of paste remaining in the aggregate. There is a high gray correlation degree among the four aggregate characteristic parameters, among them, the SP correlation degree reaches the maximum, 0.942. Samples meet the strength requirements of C30 concrete in aggregate mixing ratio appropriately and gain the best mechanical properties with RCA replacement of 30% (mass fraction).