[Objective] To provide a scientific basis for analyzing the causes of soil erosion

droughts and floods.[Methods] After building the Gini coefficient runoff uneven distribution model

annual runoff

Gini coefficient and Lorenz asymmetry coefficient(annual distribution of monthly runoff) in four hydrometric stations(Nanping

Kaishantun

Hedong and Quanhe) from 1959 to 2011 were statistically analyzed. Mann-Kendall method was employed to do trend analysis and test in annual runoff.[Results] The annual runoffs in the four hydrometric stations showed a decreasing trend during the past years. The Gini coefficient in Nanping and Kaishantun showed an increase tendency

while it showed a decrease trend in Hedong and Quanhe station. The Lorenz asymmetry coefficient in the four hydrological stations showed an upward trend

and the values were greater than 1 for the four stations in 1961

1965 and 1979

which was mainly caused by the months with large runoff volume

it is also period when drought and flood happened in history.[Conclusion] The Lorenz curve can be used to quantify and evaluate the temporal variation of runoff and its influential factor in a new perspective.