China has experienced a rapid urbanization process during the past two decades because of its fast-growing economy. In the near future, the urbanization process will be accelerated due to promotion of governments at different levels. As a major type of land use change, urban expansion, because of its potential impact on croplands, has become one of the top concerns in land planning, land management and food security of China. This paper analyzed changes in urban built-up area of 200 major cities in the 1990s, using the rank-size law, which is often employed in the study of city's population size distribution. Then, we explained the rank-size curves using theory of fractal and the results include the following several aspects. Firstly, the city size distribution in terms of urban built-up area perfectly accorded with rank-size rule, and the coefficient of determination (R2) were all more than 0.95. Secondly, according to the curve shape, we claimed that Chinese cities could be divided into three categories, i.e., large cities with an area of more than 200 km2, medium-sized cities with an area between 50 and 200 km2, and small cities, with an area of less than 50 km2. Thirdly, the China's city system in terms of built-up area is relatively well developed. and the rank-size distribution curve therefore moved in a parallel evolution manner from 1990 to 2000. Fourthly, the rank-size distribution curve revealed that the rate of urban land expansion was markedly different among these three groups of cities during the past decade. At last, this study suggested that the rank-size law could be a good tool to predict future urban expansion in China.