Abstract: This paper conducts the derivation of the urbanization curves on different hypotheses，and corrects the misunderstanding on the relationship between urbanization parameters. Under the assumption of constant urban and rural growth difference in population ( URGD) ，the time-path curve of urbanization level，velocity and acceleration would separately show a rightward“S”shape，an inverted“U”shape，and an oblique“Z”shape. Also with this constant URGD assumption，all parameters are to be set as long as two arbitrary time points of urban and rural population data are given. There is no need to turn to the linear regression between the urbanization level and time variable，and the constraint on the saturated value of urbanization level does not exist. However，under the varying URGD assumption，the urbanization curve would show certain differentiation relying on the degree of variation on URGD. With the setting of an inverted“U” shape URGD，the peak of urbanization curve would be higher and obviously shift to the left，whereas with the setting of a linear decreased URGD，the urbanization curve would appear more variation dependent upon the initial value of URGD.

Keywords: Urbanization, Urban and Rural Growth Difference in Population, "S"Shape Curve

摘要： 文章完善了城市化时间路径方程的推导，归纳了城市化时间路径曲线的趋势特征，并纠正和阐释了理论界对城市化参数关系的诸多误解。在不变URGD( 城乡人口增长率差) 设定下，城市化水平路径表现为一条右上倾斜的“S”型曲线，城市化水平速度路径表现为一条倒“U”型曲线，城市化水平加速度路径表现为一条斜“Z”型曲线; 只要存在两个时点的城乡人口数据，城市化全部参数关系均已给定，不需要求助于城市化水平与时间变量的线性回归，城市化水平变化趋势也不存在饱和值约束问题。在可变URGD 设定下，城市化曲线则表现出不同程度的变异，倒“U”型URGD 设定下，城市化曲线的峰值更高并且明显左移; 随城市化水平线性下降URGD 设定下，城市化曲线则依赖初始URGD 值而表现更复杂变异。

关键词: 城市化, 城乡人口增长率差, "S"型曲线