This paper estimates the Pareto exponent of the city size (population size and economy size) distribution, all provinces, and three regions in China in 1997, 2000 and 2003 by OLS, comparatively analyzes the Pareto exponent cross section and times, and empirically analyzes the factors which impacts on the Pareto exponents of provinces. Our analyses show that the size distributions of cities in China follow the Pareto distribution and are of structural features. Variations in the value of the Pareto exponent of city population size distribution are significantly explained by industrialization, industry structure and regional transportation infrastructure, and variations in the value the Pareto exponents of city economy size distribution are significantly explained by industrialization and regional transportation infrastructure.