Cryogenic carbon capture (CCC) is a potential technological solution to reduce CO2 emissions and achieve the needed environmental targets. CCC provides a relatively compact solution to industries where more mature technologies would have difficulty scaling down economically. However, there is a lack of research on frost formation of CO2 within packed bed systems, despite the influence of the CO2 frost layer on thermal conductivity leading to excessive cooling costs. Understanding the rate of CO2 frost growth and accumulation within a packed bed is critical to the design of the capture column. Therefore, real-time quantitative imaging becomes increasingly desirable to study the CO2 frost formation during cryogenic carbon capture, but it may be difficult by most of the traditional measurement methods. This study aims to investigate the use of an Electrical Capacitance Tomography (ECT) to monitor the real-time CO2 frost formation in a fixed packed bed. In this work, the evolution of the permittivity distribution during the capture process has been investigated in detail by experiments, elucidating the effect of the bed material type and bed material temperature. An ECT sensor was constructed to measure frost distribution to elucidate the mechanisms of CO2 frost formation by first testing on ice frost in the packed bed. The ECT images of ice formation were reconstructed by measurement data with a conventional algorithm. The results show that ECT could effectively monitor the changes of relative permittivity caused by the frost formation in real-time. With the help of an image reconstruction algorithm, the outline and position of the permittivity change area can be monitored. These results indicate that ECT has the potential to be a novel technique for monitoring CO2 frost formation during cryogenic carbon capture.