Abstract: The assessment and optimization of carbon emission levels of remediation technologies is essential for overcoming the resource and environmental constraints and promoting the development of technologies. Ex-situ soil washing technology can effectively remediate complex contaminated soils, but systematic analysis of its carbon emission characteristics during the implementation process is still lacking. Taking a lead-contaminated site as a case study, we evaluated the carbon emission level of ex-situ soil washing technology by using the IPCC emission factor method, and explored the distribution patterns and key influencing factors of carbon emission during the remediation process. The results showed that the carbon emission intensity of the ex-situ soil washing case was 32.68 kg/m³, and the fractions of direct and indirect carbon emission intensity accounted for 17.91% and 82.09%, respectively. There were different contributions in carbon emissions across various processes, with the slurry washing stage being the largest contributor, accounting for 70.56% of the total emission. Material consumption was the primary source of carbon emission, and the amount came from ethylenediamine tetraacetic acid (EDTA) flushing agent occupied 67.10% of the total emission. Sensitivity analysis revealed that the carbon emission level was highly sensitive to changes in the washing agent dosage, and optimizing the power production structure could also help to reduce the total carbon emission. Therefore, the decrease of agent dose and the measures for applying renewable energy shall be further emphasized to optimize the carbon emission of ex-situ soil washing method. The findings offer support for the development of low-carbon remediation technology for soil contamination.