Benefiting from the "two overall strategies" promotion, Guangzhou and Shenzhen which are located at eastern coastal areas of the open frontier have preferential development opportunities.In the past 30 years, Guangzhou and Shenzhen have established their status of center cities.Such status is shored up by their development.What is different is that the establishment of Guangzhou's status is a reoccurrence of history, rather Shenzhen is a newborn city which was based on the reform and opening policy.Through using classical gravity model, combining with Guangzhou-Shenzhen's city system development practice, establishing the center of the city in the Pearl River delta, identifying interactive relationship, measurement results show that algorithm and sequence rule has maintained consistency although using different calculation methods.Given the central city, hinterland cities' number and area are able to be identified.Empirical research found that:High-speed rail, do make the connected effect of the Pearl River delta cities, and the radiation effect of Guangzhou and Shenzhen are gradually strengthen, and to strengthen the ordinary railway and highway's growth driving force.In other words, Guangzhou and Shenzhen's radiation effect on the hinterland cities is greater than the siphon effect, the situation of whole linkage and clannishness development was already open.The results are still robust when using railway trains and giving weight calculation of city link index to test again.Policy implications include:Give full play to the linkage ability of rapid railway and central cities' designated radiation scope, to balance in the cluster, to regroup the relationship between government and market's action and reaction.