Abstract: Bioretention facilities are widely used in the construction of sponge cities in China, but there is a knowledge gap on their whole life cycle carbon emissions. Taking the biological retention facilities in a building community in the sponge city construction of Jiaxing City as the research object, a carbon emission accounting framework covering the whole life cycle of material production, transportation, construction and operation and maintenance was constructed. Based on the carbon emission factor method of 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories, the carbon footprint of the bioretention facilities with an operating life of 30 years was quantitatively evaluated. The results showed that the carbon emissions from the materials production, materials transportation and the construction process during the construction phase are 18 699.81, 10 129.95, 789.89 kg (in terms of CO₂, the same below), respectively. During the operation stage, the carbon emission from greenhouse gases emitted by bioretention facilities is 63 100.42 kg/a. Due to the carbon sequestration of plants and the reduction of the total rainwater runoff and pollutants, the carbon sink of bioretention facilities is 82 706.63 kg/a. The net carbon emission factor of bioretention facilities in the whole life cycle is −3.43 kg/(m²·a). From the perspective of filler selection, the net carbon emission factor of zeolite filler bioretention in the whole life cycle is less, which is −4.53 kg/(m²·a). Considering the structure of bioretention facilities, the net carbon emission factor of inverted bioretention facilities is less, which is −3.76 kg/(m²·a) during the whole life cycle. Carbon reduction for bioretention facilities can be obtained by using low-carbon materials, optimizing plant and filler, and improving the bioretention structure.