Plant coverage is a very important ecological index and it is essential for predicting soil loss quantitatively. The plant coverage of two fields located in Beijing city was measured periodically in order to analyze the errors of overhead photograph and visual estimation for plant coverage. The results showed that the overhead photo graph combined image processing was an accurate and fast method

and the maximal absolute error was less than 5 % . The plant coverage estimated by different persons have significant difference. The individual maximal absolute error was up to 40 % and average maximal absolute error for 7 persons was up to 10. 2 % .