Abstract: Scientific evaluation of the coordinated development degree of economy and environment is an effective way to realize regional sustainable development. Presently, there lack researches on national “Two Mountains” Bases which have ecological priority but small evaluation scale. Taking Ninghai County in Zhejiang Province as an example, 8 primary indicators and 32 secondary indicators closely related to economic and environmental conditions were selected to establish the evaluation index system of coordinated development of economy and environment. The coordinated development level of economy and environment in Ninghai County from 2006 to 2017 was evaluated based on the coupling coordination degree model, and its evolution law was analyzed. The results indicated that the comprehensive development index of economic development subsystem and environment subsystem in Ninghai County showed a fluctuating upward trend during the research period, and the comprehensive development level of environment was higher than the comprehensive development level of economy. The coordinated development level of Ninghai County could be divided into three stages: at the first stage in 2006-2009, the degree of coordinated development was relatively low and on the verge of maladjustment and recession; at the second stage from 2010 to 2011, the degree increased steadily to barely coordinated; at the third stage in 2012-2017, the degree was steadily improved, from primary to intermediate and then to good and superior coordinated development.