Carbon capture, utilization and storage (CCUS), as an emerging technology to reduce greenhouse gas emissions, could mitigate climate change. CO2 leakage as one of the potential risks would influence the quality of groundwater and affect the growth of surface flora and fauna, even threaten the safety of human beings living around. In order to monitor this kind of leakage and estimate the influence of leakage on shallow groundwater, it is necessary to sample the shallow groundwater continuously. Thus, a novel CO2 monitoring system in shallow well is developed. Its composition structure, working principle, countermeasures to technical problems and the procedure are introduced in detail. The monitoring system is based on the U-tube: groundwater permeates into the borehole and flows into the U-tube through a check valve; then a nitrogen cylinder pressurizes one end of the U-tube; the sample is obtained from the other leg of the U-tube. Moreover, the monitoring system is able to sample from different formation layers (the number of formation layer depends on the actual situation). It also provides data for the risk warning system in project.