[Objective] Effects of rainfall on runoff and sediment yield and the quantitative relationships were studied in small watershed of red soil region in South China, in order to provide references for controlling soil erosion and optimizing the use of water and soil resources in this region.[Methods] Based on the three years' observations of natural rainfall events of Wubeihe watershed in Wuhua County of Guangdong Province and Zhuxihe watershed in Changting County of Fujian Province in south red soil region,the methods of regression analysis and path analysis and so on were used to study the effects of single rainfall on runoff and sediments. Meantime, the calculation models were built to study the relationship between rainfall and runoff sediment.[Results] ① The results from the methods of regression analysis and path analysis were essentially in agreement:the main rainfall influence factors of runoff were rainfall, duration, 30-minute maximum rainfall intensity(I₃₀) and the interaction of rainfall and duration. The main rainfall influence factors of sediment yield modulus were rainfall, raininess, 30-minute maximum rainfall intensity I₃₀, rainfall erosivity and the interaction of rainfall and raininess. ② Multivariate linear regression model could accurately reflect the dynamic relationship between rainfall and runoff sediment in the two small watersheds. ③ The model was validated by randomly selected data using Excel, including 25 sets of data in Wubeihe watershed and 23 sets of data in Zhuxihe watershed. The results showed that the correlation between calculated runoff sediment values and the measured data was very significant(p < 0.05), especially for Wubeihe watershed, the correlation coefficient was as high as 0.950.[Conclusion] The multiple linear regression model were the best model for describing the quantitative effects of main rainfall-related factors on runoff and sediment both in Wubeihe watershed and Zhuxihe watershed.