This study conducts a life cycle assessment (LCA) of carbon emissions for recycled fine aggregate (RFA) concrete. There were six stages involved in the life cycle of RFA, including raw material extraction and processing, transportation to the manufacture, RFA concrete manufacturing, transportation to the building site, construction, and de-construction or demolition. The carbon uptake effect, due to the carbonation of RFA concrete, was also considered. The concept of “carbon-strength ratio” was introduced to comprehensively evaluate the carbon emission of RFA with different strengths. Sensitivity analysis was performed on the key parameters, including the water-to-cement ratio, RFA replacement ratio, and transportation distance, by employing three sensitivity coefficients. The results show that, under a certain water-to-cement ratio, the increase in RFA replacement ratio would decrease the carbon emission but increase the carbon-strength ratio. The higher the replacement ratio of RFA, the more sensitive the carbon emission of RFA concrete is to the change in transportation distance. Under a certain 28-day cubic compressive strength, the higher the RFA replacement ratio, the higher the carbon emission. The sensitivity analysis demonstrates that the carbon emission was the most sensitive to the water-to-cement ratio, which was followed by the RFA replacement ratio and transportation distance.