Development experience of world-wide coastal countries and regions show, joint development of the port and its hinterland area's economy is important to the regional economy's positive development. The port and the regional economy interact with each other. They bring along coastal cities' prosperity and promote the hinterland area economy's development in cluster diffusion effect and export-led effect. In order to discuss the relevance effect of interaction between the port group and regional economy, the paper selects Ningbo-Zhoushan port, which is ranking world-wide 1st in terms of cargo handling quantity, as study object for empirical study. The paper adapts data between 2007~2018 and builds up a causal relationship between Ningbo Port/ Zhoushan Port/ Ningbo Zhoushan Port and the corresponding regional economy indicator. Whereas, with software EViews10.0 and SPSS23.0, and adopting the regression analysis method and correlation analysis method, the paper makes a study on the regional economy relevance effect. The study results imply that: (1) Port and regional economies have a good interactive relationship. An increase of 1 million tonnage turnover in the Ningbo-Zhoushan port group, Zhoushan port, and Ningbo port will bring economic growth in the hinterland of 1.2848 billion, 0.2510 billion, and 1.2848 billion, respectively. The port comes into being the growth pole of regional economic growth that driving the regional economy's growth significantly. (2) The Port group area's economic growth is synchronous with port capacity growth. Correlation analysis about port cargo handling capacity and five evaluation index of GDP, GDP per capita, GDP growth rate, the proportion of tertiary industrial output-value, and total foreign trade value shows that during the years from 2007 to 2018, the correlation degree is highest between ports capacity (Ningbo Port, Zhoushan Port, Ningbo-Zhoushan Port) and GDP, the coefficient is 0.9620, 0.9920 and 0.995 respectively. (3) Regional economic growth provides necessary support to the port group. The correlation analysis outcome also shows GDP is the most important index influencing port cargo handling capacity. The continuous growth of regional GDP assures the growth of port cargo handling capacity. The regional economic development level has a great influence on the port's high-quality development.