Rock weathering and soil formation are important links of element cycling in the earth surface. The knowledge of rock weathering and soil formation rates is important for sustainable utilization of soil resources and watershed management. A typical forest watershed, located in South Anhui, subtropical China, was chosen as a case for study. Input and output of main mineral elements were monitored. Rock weathering and soil formation rates were estimated using the principles of geochemical mass balance of the elements in the watershed. Results show that with the current rainfall and acid precipitation, the average granite weathering rate is 0.696 t hm^-2 a^-1 and the soil formation rate is 0.598 t hm^-2 a^-1. That is to say, it takes more than 20 000 years to form 1 meter of soil in this area. It was found that a large amount of H⁺ was sunk into the ecosystem, but did not make stream water acidic because it was exhausted by soil mineral weathering and cation exchange. However, in the long run, it will acidify the soil. The research also found that it is necessary to re-set criteria of soil loss tolerance on the basis of the current soil formation rate.