Abstract: The aggregation effect and diffusion effect are the important dynamic mechanisms promoting the evolution of regional spatial structure. This paper uses the concentration index to measure the development status of urban system of the Yangtze River Delta region and the Beijing-Tianjin-Hebei region from 1995 to 2015. Research shows that the Yangtze River Delta is a very clear and orderly urban system, which takes Shanghai as the core and Nanjing, Hangzhou and Suzhou as the second core; in the Beijing-Tianjin-Hebei region, not only there is a low degree of coordination between Beijing and Tianjin, but also the urban hierarchy is not clear and orderly. Through the sequence- regression method, it is found that the urban system of the Yangtze River Delta is becoming more and more reasonable, while the urban system in the Beijing-Tianjin-Hebei region has not been improved significantly, and the difference of Pareto index in the two major urban agglomeration is expanding. Therefore, promoting the coordinated development of Beijing-Tianjin-Hebei region and urban agglomeration construction, should be based on the experience of urban agglomeration in Yangtze River Delta, that is, the dual-core in Beijing-Tianjin-Hebei region should play the diffusion effect better to drive the urban economic and social development.

Key words: regional economic growth, Yangtze River Delta and Beijing-Tianjin -Hebei, spatial structure, aggregation effect, diffusion effect, SEM