Radionuclide transport and risk analysis in subsurface and related control factors are important since radionuclides in environments are related to human health, and more and more people realize their significance. A lot of studies found that soil colloids are important for radionuclide transport in soil and groundwater. Soil heterogeneity and unsaturated flow are widely spread in natural environments. They are the key factors of affecting contaminant and colloid transport, and are the long-term and difficult problems for hydrologists and soil scientists. Radionuclides can move through colloid facilitated transport. Because soil heterogeneity and unsaturated flow condition in fields are very common, complex soil environments are widely spread, are extremely important for contaminant transport and remediation, and are the key factors of applying the parameters from laboratory to field scale. It is still unclear for the mechanism of soil microenvironment effect on colloid facilitated radionuclide transport. This project will attempt to do colloid facilitated radionuclide transport experiments under complex soil microenvironments, use X-ray computed tomography to observe soil structure, and combine numerical modeling with experimental data. The soil microenvironments in the experiments include soil heterogeneity and unsaturated flow conditions. The data will provide the basis for exploring the mechanism of colloid facilitated radionuclide transport under complex soil environments and develop related models to describe related phenomena. It is expected that the results from this study will be helpful for preventing colloid facilitated radionuclide into groundwater.