Large-scale construction of prefabricated concrete structures consumes a large amount of resources and energy and has become a major contributor to the environmental impact of the construction industry. Based on the life cycle assessment method, the carbon emission assessment of prefabricated concrete structures (PCS) in the construction stage was carried out, and the carbon emission intensity and level in the construction process of PCS were quantitatively analyzed. The results show that by the end of 2023, the total carbon emission of prefabricated buildings in Shenzhen has reached 4.3652 million tCO2e, and the carbon emission intensity per unit area in the construction stage is 5398.31 kgCO2e/100 m2. Among them, the contribution of the prefabricated component processing and production stage to carbon emissions per unit area is the largest, and its carbon emissions mainly come from hot-rolled steel bars and concrete. When the consumption of building materials and the change rate of carbon emission factors are the same, the change rate of carbon emissions per unit area is hot-rolled steel bars >concrete. By promoting the use of recycled steel, recycled concrete, and other green building materials, the highest carbon reduction rate in the construction process is 11.12%. According to the optimistic estimate, the carbon reduction intensity in 2025-2035 will be 943.3 million tCO2e, helping Shenzhen to vigorously develop prefabricated buildings.