The U3Si2 material is regarded as a highly potential candidate in the field of nuclear energy due to its excellent thermal conductivity and high uranium density. The Tsinghua High Flux Reactor (THFR), an advanced multi-functional high flux research reactor, uses U3Si2 as the core fuel material to achieve high research efficiency and a safer operating environment. During the operation of nuclear facility, the adsorption and migration of the radioactive fission product Cs is a key problem of radiation protection. Therefore, studying the adsorption behavior of Cs on the surface of U3Si2 is necessary for THFR safety design. However, the lack of experimental research restricts our safety analysis. In order to carry out the adsorption mechanism of Cs on the U3Si2 surface, the theoretical method Density Functional Theory (DFT) has been used in this work. Three typical Cs adsorption sites on the different surfaces of U3Si2 have been studied. It is found that the most stable adsorption is a top site on U atom ({001}-U-Si) with the adsorption energy about 3.599 eV. The adsorption of Cs atoms on the U-Si surface resulted in the shift of the surface U and Si atoms, indicating the presence of strong interactions within the adsorption system. In addition, Density of States (DOS) analyses were performed to reveal the changes in electronic states and adsorption mode. Charge Difference Density (CDD) calculations were also used to visualise the charge distribution during Cs adsorption. This work can help us to understand the adsorption behavior of Cs on U3Si2 surfaces, and can be further extended to study the entire migration process in the future.