The ¹³⁷Cs tracing method is extensively used in the research fields of soil erosion and sediment transportation.For using the method,it is very important to determine the relationship between ¹³⁷Cs and the composition of soil particles.However,at present,research on this aspect is not well conducted.So,based on the data of 39 soil profiles in different areas of red soil,this paper analyzed the relationship between ¹³⁷Cs content and the composition of soil particles using statistical methods.The result showed that ¹³⁷Cs had a positive correlation with sand and silt contents,and had a negative correlation with gravel and clay contents within 20 cm of the soil surface.Then through correlation analysis and stepwise regression analysis,it was found that in different layers,sand content was the main factor contributing to ¹³⁷Cs.The quantitative model for the relationship between ¹³⁷Cs and the composition of soil particles was constructed.The model showed that ¹³⁷Cs increased with the increasing of sand content.