Abstract: As one of the keys of economic growth, the development of cities is driven by city’s own factors and the interaction among cities. In this paper, from the perspective of economic connectivity and based on the hypothesis of the gravity model, an indicator f naming “the intensity of the external influence field” is constructed as a metric of the influence of each city from the other cities. For each city, the total value F of its f, as well as the Zipf’s exponent α of the distribution of f, is strongly and positively correlated to the city’s economy size, and more than 50% on the variation of city’s economy can be described by the changes of F and α, revealing the strong impact of city’s external economic environment on the development of city’s economy. Furthermore, from the spatial autocorrelation analysis of these external influence field indicators, we observed the remarkable heterogeneity on the trend of local spatial autocorrelations of cities at different levels, namely, the high-level cities tend to strengthen their local spatial autocorrelations but the lower-level cities tend to weaken the local spatial autocorrelations. By comparing the variation trend of local spatial autocorrelations of cities in different administrative regions, it is found that administrative regions with small population and small economic size tend to concentrate on the development of a few cities. These findings indicate that, as the indicators without any direct relationship to city’s own economy, F and α can efficiently separate the external economic influences and other influences on city to dig out the hidden patterns in city development, which is helpful in mining of the relationship between city development and the interaction of cities.