Abstract: Aiming at the enlargement of the difference of income distribution among people,this paper is contributed to study and discuss Gini coefficient,which is one of the most efficient indexes and methods to measure income inequality.The paper systematically introduces Gini’s familiar algorithm,and applies it to the measurement of the income inequality among city dwellers and to the measurement between cities and countries.Finally the data results are analyzed.

Key words: Income inequality； Gini coefficient； Difference between cities and countries；